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This has been a difficult year for wheat in many ways. And, unfortunately, the problems continue. Although some wheat fields look remarkably good considering the weather stresses they have encountered this year, in some fields various head problems are occurring. Loose smut is much more evident than it should be. Scab is developing in scattered fields throughout the state. Septoria tritici causes Septoria leaf blotch but may also cause dark blotches on heads and Stagnospora nodorum is actually more common on heads than leaves. Bacterial stripe (leaf disease) and bacterial black chaff are also evident in some fields. Finally in some fields the root disease take-all is evident as white heads in the field.

Loose smut is obvious as heads emerge from the boot and for several weeks after that. The kernels on infected heads are replaced with masses of powdery black spores. So the heads have a very obvious, black, powdery appearance. These spores are eventually dislodged by wind and rain, so later in the season the smutted stems are less evident and only the bare rachis will be left. Spores produced on smutted heads are wind carried to adjacent plants in the field and infect through the flowers. The fungus that causes loose smut survives within the embryo of wheat seeds. If infected seed is planted, the plants growing from those seeds will be infected and develop smutted heads the next season. If seed from a field that has a "small" amount of smut in one season is used for seed, the field planted with that seed may have a substantially higher level of smut. Loose smut is best controlled by planting either disease-free seed or using a systemic fungicide seed treatment.

Scab or Fusarium head blight was discussed in last week's issue of the Integrated Pest and Crop Newsletter. Symptoms of scab are evident in fields now. The characteristic symptom of scab on wheat is a premature bleaching of a portion of the head or the entire head. Superficial mold growth, usually pink or orange in color, may be evident at the base of the diseased spikelets. Bleached spikelets are usually sterile or contain shriveled and or discolored seed.

Septoria leaf blotch had not been particularly widespread or severe this season but with scattered pop-up rains and high humidity over the last few weeks this disease has come on more strongly. Foliage symptoms may be evident on the flag leaves and the dark brown to black blotches on the heads are also quite evident in some fields. Stagnospora nodorum may also cause leaf lesions but is usually more common on heads- again causing dark blotches on glumes of part or all of the head.

Bacterial stripe or black chaff is a bacterial disease that produces symptoms on both leaves and heads. Water-soaked lesions may develop on young leaves. These develop into reddish brown to brownish-black streaks on the leaves. Glumes and awns show brown-black blotches or streaks. Fungicides are not effective against bacterial stripe or black chaff so the use of resistant or tolerant varieties and crop rotation are the main management options.

Take-all is one of the more common root and crown rot diseases in Missouri. The fungus that causes this disease may infect seedlings in the fall. Symptoms are usually most evident after heading as white heads on wheat plants. Entire heads on infected plants may be bleached (white heads) and sterile. Infected plants are also stunted and slightly yellow, have few tillers and ripen prematurely. Plants with take-all typically have poorly developed root systems and roots are sparse, blackened and brittle. With sufficient soil moisture, a black-brown dry rot may extend into the crown and up the lower stem. This shiny, black discoloration of the lower stem and crown may be evident if the lowest leaf sheath is scraped off with a knife or fingernail. A management program for take-all should include planting good quality seed of adapted, disease resistant varieties, planting in well-drained sites under good seed bed conditions, rotating with nonhost crops for one to three years, controlling weed-grass hosts and volunteer wheat, using seed treatment fungicides and maintaining good plant vigor with adequate fertility.

Laura Sweets
SweetsL@missouri.edu