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Agricultural Biotechnology

Question:  Will wheat seed that hasn't emerged yet be vernalized?

Situation:  Some wheat in south central Kansas and northern Oklahoma was planted late into dry soils and hasn't emerged yet.

Answer:  Vernalization occurs when the seed has started the germination process and soil temperatures are below 48F for 4 to 6 weeks. When the seed imbibes water the germination process has started. So, the wheat seedlings do not have to be emerged when vernalization occurs.  

Question: Will low-test-weight wheat be suitable to use for seed this fall?

Situation: Due to the Easter freeze, leaf diseases, and heavy rains wheat yields and test weights in central and eastern Kansas are below normal. 

Answer: There’s no simple answer to this question. Producers who want to plant back some of the wheat they harvested from this year’s crop should have it cleaned out to a test weight of at least 56 pounds per bushel if possible. Wheat with a lower test weight may have a good germination test, and may even emerge just fine (just look at all the volunteer wheat that emerges from small or shriveled seed that is blown out the back of the combine!), but will often have lower vigor and yield potential than wheat with a higher test weight.

The effect of test weight on emergence, vigor, and yield potential will vary from year to year. When there is stress on the seedlings or young plants in the fall from freeze or drought or some other factor, the effect of higher test weight seed is often greatest.

There have been a few studies many years ago in Kansas on the effect of seed test weight on germination, field emergence, and the ultimate yield and test weight of the subsequent grain crop.

The charts below show the results of two tests done at K-State’s Agronomy North Farm in 1950 by H.H. Laude, professor of agronomy, with seed provided by Frank Bieberly, Extension agronomist.

Several conclusions can be made from this study:

* Test weight had no effect on germination

* Higher test weight seed had 20-40% improved field emergence

* Higher test weight seed emerged 4-6 days sooner

* Higher test weight seed resulted in about a 5-bushel yield increase

* Test weight of the seed had no effect on the final test weight of the subsequent crop 

In addition, in 1990 a study was conducted on seed of Arkan wheat from 25 demonstration plots around the state. Yields averaged 2.4 bushels per acre higher with the high-test-weight seed.

Field observations have shown that higher-test-weight seed results in improved vigor and fall tiller development. A note from K-State’s Department of Agronomy in 1935 substantiates this, and summarizes the situation regarding low-test-weight seed. These comments still apply to today’s varieties:

“Shriveled seed, even when it has a fairly high germination percentage, is likely to produce weak sprouts and plants that do not have enough vigor to survive unfavorable conditions. Professor J.W. Zahnley, Director of the State Seed Laboratory, states that the germinated seed of several samples of shriveled wheat with test weights ranging from 46 to 55 pounds, was characterized by weakness of the first or temporary roots. Normal wheat seedlings should have three strong roots at the end of the germination period of seven days. Many of the badly shriveled seeds produced only a single, weak primary root, or one fairly strong root and one or two very weak ones. Such seed will not produce a normal plant under average field condition. And in case of adverse circumstances, these weak plants will perish more quickly than normal seedlings.

“In cases where it seems necessary to plant wheat having test weight less than 55 pounds, it should be cleaned and graded to remove the light-weight, shriveled seed. When wheat of light test weight is used for sowing, the drill should be adjusted to avoid planting at too heavy a rate and to avoid obtaining a thicker stand than is desirable.”

If producers are planning to save their grain as seed and have it cleaned to raise the test weight, what should the minimum test weight be? How low is too low? In truth, there is no absolute minimum for farmer-saved seed, but yields and vigor are more likely to be affected at test weights below 54-56 lbs/bushel. Below 54-56 lbs/bushel, the plants are likely to have more problems in the fall and in surviving the winter. Producers planting low-test-weight seed will also have to be extra cautious not to plant the seed too deeply, since seedling vigor will be below average.

The effect of seed test weight on emergence, vigor, and yield potential will vary from year to year. When there is stress on the seedlings or young plants in the fall from freeze or drought or some other factor, the effect of higher test weight seed is often greatest.

Question:  What are the symptoms of freeze damage that we should be looking for?

Situation:  Over Easter weekend we experienced bitterly cold temperatures across Kansas. 

Answer:  Because much of the wheat was in the early stages of jointing in the northern areas of the state to near boot stage in the southern areas you'll need to look at different parts of the plant. 

If wheat was jointing, then you need to look at the stem below the node or joint. If damage has occurred, the stem will be kinked or collapsed. It will start to discolor and begin to have a dry appearance. There may be some darkening at the node. If you cut the stem open to look at the growing point, it may appear to be okay but with time it will begin to dry up and have an off-white, feathery appearance. 

Sometimes there will be no apparent stem damage, but to be certain that particular tiller is okay you'll need to cut open the stem to look at the growing point or small head. If it is damaged directly by the freeze, it will be off-white to yellowish and appear limp or flaccid. A healthy head at the jointing stage should have a crisp, clear to whitish appearance. Also, if the growing point has been damaged, it will be difficult to separate the growing point from the tissue around it. That's to say, the tissue is beginning to become mushy.

If the growing point or the stem has been damaged, the wheat will not continue to grow. The leaf coming out of the whorl will be yellow and the other leaves will turn yellow. Also, undamaged tillers will grow up past the damaged stems and cover them. So, if you see areas of the field that have continued to grow while other parts are turning yellow, then you know there is damage. 

To determine if wheat in the boot stage has been damaged, you will need to either wait until the head emerges from the boot or open the stem and look directly at the head. Damaged head will have a water-soaked appearance and can be either yellowish to white. A healthy head will be lime-green until it emerges and then it will turn darker green.

Question:  Are there any chances of winter injury this year?

Situation:  We are seeing some fields slow to green-up.

Answer:  Yes, there are chances of observing winter injury in our wheat this year.  Wheat that was planted into fluffy soil and planted more shallow than normal appears to be suffering a bit. The fluffy soils allow the cold to penetrate and cause injury. Also, where there was winter grain mite feeding late last fall those fields appear to be a little slow to green-up. 

Question:  How long can wheat stay under snow and ice and still survive?

Situation:  We've had wheat covered with snow and ice for more than a month in northwestern Kansas.

Answer: There's no real good answer to this question. Ice is the potential problem and not the snow at this point. Wheat that is dormant can tolerate ice cover longer than if it wasn't dormant. An ice sheet cuts off the gas exchange and plants eventually die from the byproducts of anaerobic respiration. A Canadian study indicated plant losses after 4 to 6 weeks covered with a sheet of ice. 

In our case, time will tell. 

Question:  What's making the wheat turn yellow?

Situation:  There are concerns about the wheat leaves turning yellow in some areas of the state. The wheat doesn't appear to be growing very much and some might say the wheat is going backwards.

Answer:  Cold weather will make the leaves turn yellow and sometimes leaves will turn purple when they are under some stress, but I don't think cold weather is the real problem.  I think we're seeing some drought-induced nitrogen deficiencies symptoms and just plain drought stress. The lower leaves are turning yellow from the leaf tip and moving back on the leaf blade. The root systems are not extensive and in many cases there are very few roots. The first few inches of the soil are very dry. So, considering these conditions the symptoms point to the effects of dry soil.

Question: What's the germination of this year's wheat seed?

Situation: With the poor growing conditions there are concerns the wheat seed may have lower germination than usual.

Answer:  This year’s wheat crop is averaging about 97 percent germination in laboratory tests so far, which is very good. For the first several weeks after harvest, it’s important to make sure the wheat is pre-chilled before taking a germination test. The lab will do that on a routine basis. But producers testing their seed at home should also pre-chill the wheat by putting it in the refrigerator at about 40 degrees for 5 days.  Wheat has a physiological characteristic called post-harvest dormancy. If you take a germination test immediately after harvest the germination can be quite low.  The pre-chilling treatment breaks the post-harvest dormancy and will allow the seed to germinate normally.

There is some difference among varieties regarding how long their post-harvest dormancy period is. Hard white wheats with poor sprouting tolerance, for example, have almost no post-harvest dormancy. They will germinate almost as soon as the seed is harvested. Other varieties, such as Overley, have a relatively long post-harvest dormancy, and may not germinate well for five or six weeks after harvest unless the seed is pre-chilled. By Labor Day, all varieties will have lost their post-harvest dormancy and should germinate unless the seed is defective in some way.

If there is any question about the viability of the seed, it is well worth the $15 it costs to have the seed tested for germination by a certified seed laboratory. This is especially true in areas where there was freeze damage, severe drought, a rain delay at harvest, or scab on the wheat last year.

Question: With the warm weather we had in January, did the wheat vernalize?

Situation: January, 2006 was the warmest January on record in Kansas.

Answer:  Vernalization is a cool-period requirement that winter annuals, such as wheat, need to switch from vegetative to reproductive stages. Freezing temperatures are not required, but rather, temperatures at 48F or below will initiate vernalization. Varieties differ on the length of the cool period required, but generally, 3 to 6 weeks will be sufficient for complete vernalization. Also, wheat doesn't have to be emerged to start the process, it only has to have initiated seed germination.

Well, back to the question.  The wheat was probably already vernalized by the time January got here because December was fairly cool.  Generally, that's the situation with wheat planted at optimal planting times and normal growing conditions . . . wheat will have been vernalized by Christmas because the late fall and early winter are cool enough for the process to have occurred.  

Question:  What are the disadvantages of planting wheat earlier than the recommended dates for a specific area? 

Situation:  Some producers, especially in western Kansas, start planting when they receive rain in early September. 

Answer:  In western Kansas, we're very concerned that earlier than normal planting will cause excessive fall growth, use up available surface moisture and ultimately result in winterkill damage. This is especially concerning when we have a late fall killing-freeze and the wheat continues to grow and use moisture later in the season. 

There are other problems associated with early plantings. Wheat streak mosaic is a disease that comes to mind. Some producers wait until the last possible moment to control volunteer wheat and if a field of volunteer wheat is within a half-mile or so of a newly planted wheat field, the likelihood of the newly planted field becoming infected with wheat streak mosaic increases tremendously. (Of course, this could also occur with late-plantings if volunteer wheat is nearby.) 

Last year in western Kansas, with the excessive fall growth and good moisture conditions, a considerable amount of leaf rust was observed. Early plantings tend to suffer from Hessian fly infestations because there's a "green" bridge between wheat crops that can harbor Hessian fly.  Also, we often see more crown/root rots associated with early plantings into warm soils.  

Question: Why did no-till wheat after wheat not fare as well as more conventionally-planted wheat this year?

Situation: Some producers observed that their no-till wheat had thin stands and plants were stunted and yellow.

Answer: There are several issues that arise with no-till wheat. Seeding rate, seeding depth, planting speed, planting date, and nitrogen applications are the first issues that come to mind. The thin stands could be caused by a number of things. The seeding rate might not have been high enough. When planting no-till into crop residues the seeding rates should be increased. It is not unusual to see seeding rates in the 90 to 120 pounds per acre range even with normal planting dates.

This past year we observed that seeding depth and planting speed were related. The faster the planting speed the shallower the seed was placed and with the dry conditions we experienced this past spring, those shallowed-seeded plants did not root very well and showed considerable drought stress. Also, sometimes the soil under no-till situations is harder, it’s more difficult to penetrate to the desired seeding depth. We can see more winterkill or winterdamage when wheat is planted too shallow.

This year, late-planted wheat showed more effects of the late April-Early May freezes than wheat planted at a more normal time. Late-planted wheat didn’t have a closed canopy and the cold air was able to freeze the lower areas of stems.

However, nitrogen is probably the most important reason no-till wheat didn’t look so good. More precisely, how much nitrogen was applied and how was it applied? With heavy crop residues, such as with wheat residue, we’re concerned with immobilization of the broadcast applied nitrogen. That’s to say, the nitrogen can be tied up on the residue when it is broadcast applied and it won’t be readily available to the growing wheat crop. Thus, there is less total nitrogen available which could result in nitrogen deficiency symptoms, such as yellow plants. For example, if a producer normally applies 60 pounds N per acre and 20 pounds N per acre are immobilized, the crop will not have enough nitrogen to produce a good grain yield.

So, how do we overcome nitrogen immobilization in no-till wheat? If a producer is going to broadcast the nitrogen, then the only solution is to increase nitrogen rates by at least 30-40 pounds per acre. The other solution would be not to make a broadcast application, but rather, inject the nitrogen below the residue into the soil. This would eliminate the immobilization problem caused by the standing residue. The big question is, "how does a producer go about doing that?" Well, nitrogen could be injected before wheat planting or it could be injected at planting, but that would require some modifications of the drill.

There is another aspect of nitrogen that we have to consider and that is the fact that in some fields, producers have removed some tremendous wheat, grain sorghum, and corn crops the past few years. In these cases soil nitrogen levels have been depleted and the normal nitrogen applications have not been sufficient which results in deficiency symptoms.

Question: What symptoms do you look for when assessing freeze damage?

Situation: Over the last two weekends of April and early May temperatures ranged from the low 20's to 32, while wheat was in various developmental stages. 

Answer:  Initially, the first symptoms were leaf burning where the leaf tips turned brown. Some leaves actually appeared black and water-soaked. My first thought (or hope) was we had only cosmetic damage and no real freeze damage. But now we can see fields, especially low lying areas, that have an odd color to them- sometimes the leaves have purplish color, but mainly leaves are turning yellow to bright yellow, while others have some necrosis. As you know, we’re most concerned when temperatures drop below 32 when the wheat has headed and into the flowering stage.

It takes about 5-7 days for the head to fully extend above the flag leaf and before flowering begins. Flowering will begin in the spikelets (farmers call them rows or meshes) about 2/3 up the head and will progress up and down the head over a 3-5 day period. Within each spikelet there are generally 2-5 florets, but usually only 2-3 florets will produce kernels.

Inside a healthy floret just prior to flowering or pollen-shedding, there are three, lime-green anthers and a stigma that has two, fluffy-white branches. (If you look inside a floret soon after heading, the stigma will not be open yet.) The anthers are pushed upward as the filaments or stems to which the anthers are attached elongate, pollen inside the anthers is released and lands on the stigma. At that time the anthers have started to change from their lime-green color to a yellowish color. The anthers continue to elongate and can be seen outside the florets where they are yellow to white. This is how flowering normally proceeds and within ten days after flowering, kernels should be nearly their full size.

When freezing temperatures occur at this stage there are several things that can occur. With temperatures that are at or below 32 F the anthers, which are more sensitive to cold than the stigma, can be damaged which will lead to floret sterility. The first visible freeze-damage symptom to the anthers is they will become shriveled and twisted while they still have their lime-green color. This can be detected with a hand lens within 24 hours after the freeze. If there is damage, over several days the anthers will not elongate and they will continue to shrivel and turn whitish-yellow. In this situation, pollen wasn’t shed, but if the stigma was not damaged it could still be receptive to pollen from anthers in other florets that weren’t damaged. However, if the stigma was damaged, it will not open to expose its two, fluffy branches and it will become shriveled and whitish-brown.

Not all wheat was in the heading to flowering stage when the freeze occurred. We generally think wheat is safe if it’s not heading when it freezes, but that’s not necessarily the case. Wheat in the boot stage, while it can tolerate colder temperature, can also be damaged. With light damage the head will become trapped in the boot as it emerges and the head will have a gnarly appearance. To determine if there’s more severe damage, you need to look inside the florets to assess the anthers and stigma. If the anthers are white and shriveled then damage has occurred. Sometimes the head (in the boot) will already have a yellowish to whitish color if there’s damage instead of a nice crisp, green appearance. These damaged heads will continue to emerge from the boot as if nothing is wrong, but you’ll be able to see the color differences. Sometimes there’s partial damage to the head, that’s to say, some spikelets will be damaged while other spikelets are fine. The glumes will be yellowish to whitish and papery and when you try to open the glumes to check the anthers and stigma the floret or whole spikelet may fall of the head.

Also, we’re seeing damage to wheat in the pre-boot stage, especially in late planted fields that didn’t have good canopy coverage or in no-till fields where the residue kept the heat from the soil from rising into the canopy. It’s a little more difficult, but if you slice the stem open just above the uppermost node to look at the developing head you will see a silvery-white cast on a damaged head. The glumes might have a crinkly, papery appearance instead of having a nice lime-green, crisp, turgid appearance of a healthy head.

If you see the leaf coming out of the whorl is yellow or chlorotic, the growing point is probably dead. You will need to cut open the stem above the uppermost node to look at the small head. If there’s damage, you might have difficulty separating the head from the surrounding leaf tissue. If the head is whitish-brown to brown, then you know the head is dead.

In fields that are turning yellow, look at the lower stems. Pull the leaf sheaths back to assess the stem. If the stem between the nodes has collapsed or discolored or if there’s discoloration at the nodes, that’s freeze damage. This damage restricts nutrients from moving upward which causes the leaves to die. I’ve noticed some yellow areas in fields that has been caused by powdery mildew, so you’ll need to check for those symptoms. If the wheat hasn’t grown or continued development since the freeze, that’s an indication there’s damage.

See the publication, "Spring Freeze Injury to Kansas Wheat," C-646 and "Adopt a Wheat Field" on the K-State Wheatpage (www.oznet.ksu.edu/wheatpage) for more details.

Question:  Why is there more Hessian fly damage this year compared to other years?

Situation:  Last fall, we saw plants with stunted tillers and thick, dark green leaves. Some plants had died or were dying. 

Answer:   It should be mentioned that for the past several years we've seen stem breaking or lodging caused by Hessian fly, but not so much plant stunting and dying in the fall. 

There are three main reasons why we are having more Hessian fly damage this year. First, we are seeing more damage in early planted wheat than later or normal planting dates. That's because more Hessian fly adults are present that time of year and if volunteer wheat is present in late summer and early fall, that allows for another hatch which increases the number of adults to infect the newly planted wheat crop. Second, there is more wheat planted no-till into standing wheat stubble now than in past years. If there was Hessian fly already present in the wheat stubble, the lack of tillage allows more insects to survive to infect the new crop. Third, the prominent wheat varieties planted in Kansas do not have resistance to Hessian fly. Jagger and Jagalene are very susceptible to Hessian fly.  Resistance is a very effective method of reducing Hessian fly damage.

When you combine these three reasons, early planting, no-till planting into wheat stubble, and susceptible varieties, it is no small wonder we are seeing an increase in Hessian fly damage. 

Question:  Will we see much winterkill damage this year?

Situation:  Some areas of the state have considerable fall growth, Hessian fly infestations, we had an unusual fall leaf rust infection, and we had some very cold days in late December and January. Producers are concerned this might have set up the wheat for winterkill damage. 

Answer:  Generally, we don't have too much actual winterkill. Winterkill is when the wheat doesn't survive the winter.  We see winterkill on terrace tops or north facing slopes when soils are very dry and soils temperatures at the crown are 10 degrees F or below.  The temperature of dry soils fluctuate more rapidly and drops lower when very cold air temperatures arrive. Water in soils acts as a temperature buffer so that soil temperatures don't get too cold when air temperatures are very cold. So, wet or moist soils will protect wheat plants from winterkill damage. 

We have "springkill" which is when temperatures warm in late winter and the wheat starts to green-up, then bitterly cold weather quickly moves across the state. As wheat greens-up, it naturally loses its winter hardiness and is subject to rapid drops in temperature.  We could see that type of damage later this winter and early spring. Also, adding to the potential problem is the fact we have a variety like Jagger, that greens-up very quickly with warm temperatures and that makes it more vulnerable to cold temperatures. 

We worry about winterkill damage after excessive fall growth because that growth removes moisture from the soil. But if the soil remains wet we shouldn't see anymore winterkill damage. Tillers that have Hessian fly "flaxseeds" in them may not survive the winter. The plants that were infected with leaf rust this fall and were very chlorotic (yellow) will probably survive the winter. But plants may be weakened. We haven't seen fall leaf rust infection as severe as it was, so we don't know exactly what will happen to those plants.  

Question: How many wheat plants per foot of row are needed to leave a thin stand?

Situation: The recent rains in western Kansas have caused soil crusting which has led to some stand establishment problems for wheat that was planted just prior to the rains. Producers are wondering if the number of plants per foot of row is adequate for excellent yields or should they replant those fields.

Question: What concerns should I be aware of when considering no-till, continuous wheat?

Situation:  I know some farmers that have been successful no-till planting wheat into wheat stubble.  The conventional wisdom is that it won't work. What are they doing to make it work?

Answer:  One major obstacle to overcome in a no-till, continuous wheat situation is the foliar disease, tan spot, because it carries over on the wheat stubble.  Tan spot can cause serious yield losses. In the past, plowing took care of the spores on the residue, but with reduced-tillage or no-tillage systems there is potential for high levels of tan spot spores to be present to infect the next crop. We haven't seen very high incidences of the disease recently, which is due to the fact Jagger has been widely planted.  Fortunately, Jagger and other varieties such as, 2137, Karl 92, and Overley have good levels of tan spot resistance.  When these varieties are planted, especially the first year, the levels of tan spot inoculum are generally lower than if a susceptible variety had been planted.  When the second planting occurs into this wheat stubble there is very little inoculum present to cause a problem. Thus, it's important to use a resistant variety.  If a susceptible variety has been planted, an option would be to use a fungicide to control tan spot. Most producers that no-till plant into wheat stubble only plant wheat twice in this system before they rotate to another crop.

Other management items to consider are: making sure the drill penetrates the wheat stubble to get good seed-soil contact; delaying planting later in the optimum planting range to reduce the potential of Hessian fly and allowing time to control the volunteer wheat; increasing the seeding rate by 10-15 %; banding a starter fertilizer with the seed; and increasing the nitrogen rate the second year by 15-20 % if it is broadcast applied.  This will overcome the immobilization of nitrogen by the wheat stubble. If the nitrogen is knifed into the soil either prior to planting or at planting, use the recommended fertilizer rate. 

Question: How does rain during harvest affect test weight?

Situation:
For the first few days of wheat harvest the farmer is pleased that the test weight is 60 pounds per bushel. But unfortunately, harvest is delayed a couple days due to rain and when harvest resumes the test weight is 57 and 58 pounds per bushel. What happened?

Answer:
First, remember that test weight is a measure of how much grain weight that can be placed in a given volume.
Prior to the rain the wheat kernels were smooth and well-shaped and packed well into a bushel. When it rains kernels swell and upon drying the kernels do not shrink back to their original volume and shape and smoothness. This results in more space between kernels and they will not pack into a bushel as well as they did before the rain, thus, causing a lower test weight. But this does not reduce the total number of pounds of grain produced from an acre. That’s to say, there’s no real grain yield loss.
However, after an extended rainy period some wheat may begin to sprout in the head (the kernels begin to germinate). When this occurs test weight is reduced because of seed respiration and the germination process, so there could be a real loss of dry matter.