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Fig. 1. White heads occur in patches. 
(photo by Bill Willis)

    Fig. 2. Black discoloration of roots and lower stem  (photo by Bill Willis)

SYMPTOMS

Take-all root rot occurs throughout Kansas, but is most common in the central part of the state. Symptoms are often first detectable around jointing time. Affected plants are stunted and yellow compared to healthy plants. This early phase of take- all usually goes unnoticed. If take-all is suspected early in the season, plants can be diagnosed in the Plant Diagnostic Laboratory by the presence of take- all fungal mycelium on the roots and crowns.

After heading time, take-all symptoms are much easier to detect. Whole plants begin to die and turn color prematurely (Fig. 1). The white heads contain little or no grain. Plants may die individually or in large patches. Patches usually occur in wetter areas of the field. Occasionally whole fields are killed and this is how take-all gets its name.

Since take-all is a root rot, affected plants pull out of the ground very easily. Diagnosis can be confirmed by the dark black discoloration on the roots and at the base of the stems (Fig. 2).

Take-all can be confused with Cephalosporium stripe, drowning, dryland foot rot, strawbreaker foot rot, winter injury, and crown rot symptoms. However, only take-all has the shiny, dark black discoloration on the lower stems.

LIFE CYCLE

The take-all fungus survives between wheat crops in undecayed crop residue, on grassy weeds, and on volunteer wheat. Since the take-all fungus is short-lived, take-all is primarily a problem in continuous wheat. Take-all builds up slowly, so it's usually the third or fourth year of continuous wheat which is severely damaged.

In the fall, the fungus moves from the old residue onto the roots of young wheat seedlings. This requires good moisture and close contact between the old residue and the new roots. There is evidence that the take-all fungus also spreads from plant to plant along root bridges, which may help explain why take- all occurs in patches. Take-all infestations often originate from weedy grasses in ditches or waterways. Pieces of infected roots and crowns are simply dragged into the field during tillage. Smooth brome, cheat, wheatgrass, and wild barleys are all possible sources. The take-all fungus also produces airborne ascospores which may play a role in initiating new infections. Take-all is not carried in the seed or by insects.

CONTROL

The weak link in the take-all life cycle is survival between crops. Therefore, crop rotation is the ideal control for take-all.

Any other crop makes a good rotation except barley and brome grass since they are susceptible to take-all. A good rotation would be two years of wheat followed by one or two years of a different crop. A full year of fallow is also an effective rotation. It is important to control weedy grasses in the rotational crop, since many grasses are hosts of take-all. If crop rotation is not feasible, we can try to reduce the summer survival of the take-all fungus. Burning followed by one or two tillage passes will hasten the breakdown of the wheat residue. Plowing may bury the residue deep enough that the take-all has trouble attacking new seedlings. Clean-tilled fields also achieve higher soil temperatures, which are detrimental to survival of take-all. Of course, these methods are not appropriate for highly erodible land.

Late planting is sometimes helpful because it gives more time for the take-all fungus to die out. It also leaves less time for the new seedling roots to penetrate the old residue and become infected in the fall.

Continuous wheat producers may get help from a phenomenon called "take-all decline." After take-all severity peaks in the fourth or fifth year of continuous wheat, severity may then decline due to parasites of the take-all fungus itself. Afterwards, take-all severity usually remains low enough to tolerate. However, just one year of rotation to a different crop means you have to start all over again. That means you have to suffer high losses for several years before you regain take-all decline. Take-all doesn't like acid soils and is suppressed when the pH gets much below 6.0. When continuous wheat is limed, severe take-all often results. It is good practice to combine liming with crop rotation.

Unfortunately, there are no hard red winter wheat varieties with resistance to take-all. However, soft red winter wheat varieties Auburn, Clark, Lincoln, and Twain have been reported to have tolerance to take-all. We have not yet tested this claim for Kansas conditions.

A seed treatment called Baytan gives partial control. It is fairly expensive, must be applied by specially trained personnel, and shortens the coleoptile. Since control is only 20 to 30%, it may be of limited appeal to Kansas producers. Dividend also gives partial control of take-all but doesn't shorten the coleoptile.

Split applications of nitrogen have shown some suppression of take-all compared to putting all the nitrogen on in the fall. Ammonia nitrogen seems to suppress take-all compared to nitrate nitrogen. Maintaining adequate levels of other nutrients helps the wheat grow new roots when take-all nibbles them off.

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Web updated 9/01/06
Web comments to jpierz@ksu.edu