ISSUE 8 June 22, 2000
SMALL GRAIN DISEASE SURVEY UPDATE
The latest survey reports across the state still indicate relatively low disease severity in most wheat crops. Last weeks rains and this weeks deluge in parts of the Red River Valley certainly may change the story. A week to 10 days is necessary for disease infections to become evident, once environmental conditions trigger fungal sporulation and spread. Diligent scouting will be necessary now and during the next few weeks to determine disease threat.
Survey results, as of June 19, indicate that tan spot is still the most common disease in wheat, with incidences high, but severities generally low, averaging between 5-10 percent. However, the severities are much higher in fields planted into wheat stubble. Severities of tan spot are highest in the NC, NW and SW areas of the state, where shorter rotations between wheat crops are more common. Septoria (Stagonospora) blotch also is common in the NC and NW districts.
Leaf rust detections are still few and severities remain in the 1-2% level. Leaf rust was detected on winter wheat at Carrington, but no leaf rust was detected yet in counties in the NW and NC areas. BYDV and WSMV are becoming more evident in the SW district. English grain aphids were detected on heads of winter wheat at Minot, but overall, weather has not been good for aphid development. Loose smut also was detected in headed wheat in the SW area. Head scab has NOT been reported yet in winter wheats that have finished flowering.
Barley fields are also showing some low levels of spot
blotch and net blotch in wetter areas.
Last weeks rains plus Mondays heavy rains are going to favor fungal spore production and disease development. Small grain producers MUST assess the condition of their crops before making a fungicide decision.
1) A waterlogged field with long standing water has a high potential for root rot and crown death. Such a field is not a good candidate for protecting against leaf and head diseases.
2) Crops flattened by wind, heavy rain, or hail may not recover enough to warrant fungicide treatment. Wait a few days to assess how the crop recovers. NDSU does not have data on the effect of fungicides on severely lodged grains.
3) Crops in the early heading and flowering stages will be the best candidates for fungicide protection. Winter wheat crops that have already flowered and are in kernel development may be beyond the need for fungicide application.
Spring wheat crops with high yield potential and at the early flowering stage have the highest potential to benefit from fungicide treatment. Head scab is a looming threat, because the saturated soils are going to favor spore production and the high humidities and dew points necessary for disease development.
FUNGICIDE TIMING FOR SMALL GRAINS
NDSU fungicide research has consistently shown that the optimum timing of fungicide application for Fusarium head scab control is at early flowering for spring wheat and durum, and at early full head emergence for barley. These stages equal Feekes 10.51 for wheat and durum, and Feekes 10.5 for barley (barley flowers while head in boot). Early flowering means that 10-25% of the main stems are flowering, while tillers have not started yet.
These fungicide timings also have given excellent control of tan spot, Septoria leaf blotch, and leaf rust. Our leaf disease pressure so far hasnt warranted a fungicide application at boot stage.
See Crop and Pest Report #3, May 18, 2000 issue, for more information on fungicides registered for wheat and barley and for preharvest intervals.
The Small Grain Disease Forecasting System will be down as long as the NDSU web server is down. Please check your internet periodically for renewed access to our programs.
Extension Plant Pathologist
PLANT PEST DIAGNOSTIC LAB
One of the pest problems commonly submitted to the lab on trees and shrubs is caused by mites in the family Eriophyidae. These mites are more closely related to spiders and as such are not actually insects. They cause several types of symptoms and have been referred to as gall mites, bud mites, and blister mites. The eriophyid gall makers are the more common pests in the lab.
These eriophyid mites are extremely small, about 1.5 mm in length, and cause plants to produce identifiable galls that may be bladder-like, spindle-like, or more like dense hairy masses or beadlike growths referred to as erinea. A brilliant reddish color may be associated with these galls making them quite obvious. Early spring foliage is affected and often it is the leaves next to the trunk and larger branches that first show symptoms.
Not much is known about the life cycle of many of these mite species. Many of them have been identified and described based on the plants typical response to infestation. The galls formed provide a protective haven for the mites to mature, at which time they will move out from the gall and to newly developing foliage where new galls are produced. The mites induce the gall formation in the host plant, and the mite activity is not generally considered detrimental to the health of the tree, despite the dramatic appearance. Treatment for these pests is rarely recommended, and as the season progresses, mite activity decreases allowing for trees to fill in with unaffected foliage.
Maples are one of the more commonly affected host plants and all three of the gall types - spindle, bladder, and erineum - occur on maple; however there are many other host trees and shrubs that may show symptoms. One of these is Viburnum. An as yet un-named species of eriophyid mite has been identified on Viburnum that causes a hairy proliferation of trichomes, or plant hairs, on the underside of the leaves. This mite may also cause the leaves to curl and crinkle. The Bismarck area has reported a high incidence of this problem and it has not been determined if the mite is actually causing dieback and symptoms severe enough to result in damage to the host. Unfortunately, by the time symptoms are observed, it is too late to control the pest. Researchers at NDSU continue to monitor incidence of this Viburnum pest and study the life cycle to determine the extent of symptoms and injury that it causes. Recommendations for management will be published as more information is accumulated and studied. If symptoms fitting this description are observed, it would helpful to send samples to the diagnostic lab to help document the location and occurrence of this pest.