Wheat emergence and seedling development concerns
* Leaf rust. If leaf rust infects young seedlings in the fall, the plants may turn yellowish. Severe fall infections of leaf rust are not common in Kansas, but can occur. Producers will be able to see the small brown pustules on the leaves. Tan spot can also cause wheat to turn yellow in the fall. These seedling infections of tan spot are often associated with wheat sown into heavy wheat residue. Viral diseases, such as soil-borne mosaic, wheat streak mosaic, and barley yellow dwarf, can infect wheat in the fall. Some yellowing can occur in the fall but in most cases the severe yellowing symptoms do not show up until early spring. It rarely, if ever, pays to treat fields with fungicides in the fall for leaf rust or tan spot, even if those diseases do cause yellowing. Cold temperatures in the winter normally cure this problem.
* Cold weather. When temperatures are quite cold at the time wheat emerges, it can result in yellow banding on the leaves. If this is the cause of the yellowing, symptoms should eventually fade away.
* Greenbugs or bird cherry oat aphids. These insects most commonly infest wheat sometime after the first freeze and before Christmas. They can cause plants to turn yellow and be somewhat stunted. These symptoms can occur in the fall, but don’t usually show up until early spring. Often, greenbug and bird cherry oat aphid infestations occur in patches in a field, not uniformly distributed. Both infestations are usually initiated by one winged female landing on a susceptible wheat plant. That female starts to produce more females, which then produce more females, and so on. The resulting infestation often radiates out from the initial infested plant in a roughly circular pattern.
* Hessian fly. Seedlings infested by Hessian fly in the fall are typically not yellow, but are often stunted. Affected plants usually have an unusually large, broad greenish leaf for about a month in the fall. Stem elongation is typically much shorter than normal.
* Flea beetles. These tiny insects cause whitish streaks on the upper surfaces of leaves. If streaking is severe, plants may die.
Causes of seedling death or loss of leaves
If leaves are being lost, or the plants are sickly or have died, it is important to find out why before replanting. Some of the most common causes of seedling death, sickliness, or loss of leaves include:
* Seedling blight. This is one of the most common causes of post-emergence seedling death or sickliness. The root system or coleoptile region may be diseased or dead in infected plants. Several fungi cause seedling blight, and these diseases are often worse on early-planted wheat. Seedling blight may not kill the seedlings outright, but can lead to later problems with common root rot, crown rot, sharp eyespot, and dryland root rot (also known as dryland foot rot).
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