ISSUE 12 July 18, 2002
WHEAT LEAF RUST UPDATE
Leaf rust levels are increasing on spring wheats throughout the central, east central and northeast parts of North Dakota. The general area of greatest occurrence, as observed by the NDSU IPM crop scouts, is indicated in the following figure:
Leaf rust also may be occurring in other counties than indicated above, but these counties were not included in the survey the last week.
Growers and extension and industry agronomists report that the ‘Ingot’ hard red spring wheat appears to be the hardest hit at this time, although substantial amounts of leaf rust are also being reported on ‘Russ’, ‘Parshall’, ‘Gunner’, and ‘Reeder’. Boots, pant legs and truck wheel rims are coming out of fields coated with the rust spores. Leaf rust is also being observed on other varieties, such as ‘Norpro’ and ‘Alsen’, but to much lesser amounts.
Fields sprayed earlier with fungicides prior to rust development on the flag leaf are looking good. Crops in the milk to soft dough stage or ones with 10-15% rust or more on the flag leaves are too "far gone" for application of fungicides now. Growers should concentrate on the later fields, ones in the boot to heading stage. Fungicide decisions for these fields should then be made based on yield potential and rust occurrence.
SMALL GRAIN SURVEY UPDATE
NDSU IPM field scouts are finding tan spot and leaf rust to be the most common diseases on wheat crops. Some Septoria infections are starting to be observed and loose smut levels greater than 1% are now being detected in some fields. Spot blotch and net blotch in barley are apparent, although still at relatively low levels. Fusarium head blight or scab had not been recorded by field scouts yet last week, but some incidences should become apparent this week. I have only observed incidences of scab at less than 1% in fields in Richland and Cass counties. I have also observed trace levels of barley yellow dwarf virus symptoms in fields in SE and EC North Dakota. More information on NDSU field survey results on wheat, barley, canola, sunflower, soybeans and grasshopper detections can be found at the following web site, which is updated weekly:
SMALL GRAIN DISEASE FORECASTING UPDATE
The small grain disease forecasting web site:
updates disease risk daily and indicates if favorable weather conditions occurred in the past 24 hours for infections by the leaf rust, tan spot, Septoria blotch and Fusarium head blight fungi. Risks that are very low one day may change dramatically within a day if rainfall occurs or temperatures change. Currently, the highest risk for Fusarium head blight is in the parts of the Red River Valley that got the most rain over July 7-10. Many crops currently in high risk areas are past the growth stage for fungicide treatment.
Extension Plant Pathologist
BRAVO WEATHER STIK ON MINT
A section 24(c) special local need label has been granted to Bravo Weather Stik (chlorothalonil, Syngenta) for application on mint for management of rust and Septoria leafspot in North Dakota. Bravo Weather Stik may be applied at 1.40 pints/acre when plants are 4 to 8 inches high and can be repeated at 7 to 10 day intervals. Bravo Weather Stik should not be applied more than 3 times per season, and should not be applied within 80 days of harvest.
QUADRIS ON SAFFLOWER
A section 18 emergency exemption label has been granted to Quadris (azoxystrobin, Syngenta) for application on safflower for management of Alternaria leaf spot in North Dakota. Quadris may be applied at 9.2 oz/acre at the onset of the first flower ray on the primary head on the first plant in the field.
SEPTORIA LEAF SPOT ON SUNFLOWER
Several cases of Septoria leaf spot, caused by Septoria helianthi, on sunflower have been reported in the last week. Symptoms of the disease include angular to diamond-shaped brown lesions. Lesions will be found on the lower leaves first, and newer lesions may have a yellow halo surrounding them. The high temperatures and rainfall encountered in parts of the state lately, may be partly responsible for the development of the disease. Crop rotation and use of disease-free seed will help manage the disease.
Extension Plant Pathologist
TESTING SOYBEANS FOR PHYTOPHTHORA ROOT ROT
Phytophthora sojae, the pathogen that causes Phytophthora root rot is a water mold. It requires free moisture, or water, for the swimming spore stage to infect roots. Fields that were flooded or excessively wet at planting are at high risk. This disease can cause pre-and post-emergence damping off, but symptoms may also be exhibited on older plants. Soybean cultivars vary in their tolerance to this pathogen, with symptoms being most pronounced on cultivars with low tolerance. Symptoms on these plants include interveinal and marginal yellowing, chlorosis of upper leaves and wilting. Leaves often remain attached after the plants die. On these plants, stem lesions may progress up the stem as high as 10 nodes, appearing brown to purple and sometimes having a stripe-like appearance. On more tolerant plants, the only symptoms, initially, may be discoloration of the taproot and breakdown of the secondary roots. These plants will likely begin to wilt, turn yellow at the top, desiccate, and die under the higher temperatures that are typical of late July and August; and they can go down rapidly in this weather.
The Plant Diagnostic Lab can confirm Phytophthora root rot but the success rate for isolating the pathogen depends on the quality of the sample submitted. If you suspect this root rot pathogen on soybeans, it is best to dig plants and bring in, or mail, a small amount of soil around the roots with the rest of the plant. This soil and root ball can be enclosed in plastic and secured firmly (but not too tightly) with a twist-tie, rubberband or similar device. The foliage of the plant should not be wrapped in plastic. It takes about a week for these cultures to develop.
In addition, the lab will now be able to offer race-typing for Phytophthora on soybean. The differentials used for this test are being collected this season so we will not have results until this fall. However, it is important to get the plants into the lab now so cultures can be established from infected plants to be tested for race later. If you have any questions on how to sample or how the race-typing works, please contact the lab (701.231.7854 or firstname.lastname@example.org ).
On an unrelated note regarding soybeans, we had a sample from the Minnesota side with downy mildew. This disease can be seedborne, caused by Peronospora manshurica. It shows up first as yellow to white spots on the upper surface of the leaf with white to gray fuzzy growth on the underside of the leaf, corresponding to the spots on the upper surface. It does not usually result in serious crop loss (Iowa reports generally no more than 10% loss), but there are no foliar treatments for disease. Management requires plowing under crop debris and fungicide seed treatment. To view disease images, go to the NDSU Plant Diagnostic Lab web page:
and click on the links for Plant Disease and Diagnostic Information, field crops, soybeans.
NORTH DAKOTA SOYBEAN DISEASES WEB SITE
Soybean is a major oilseed crop with over 2 million acres in the state. Diseases are now important factors in the management of this crop. Root rot damage is starting to appear in fields and growers will be asking questions about disease identification and control. A web site describing important soybean diseases in North Dakota can be found at:
The web page should be useful when addressing questions on soybean diseases. There are six diseases currently described with images and a section on seed treatments. Information on disease biology and control is included in each section Additional disease descriptions will be added over the next year. Research data from the Soybean Pathology program at NDSU will also be added to this site in the future.
Anyone working with soybean is asked to report any potential cases of soybean cyst nematode (SCN) in North Dakota. SCN is the most important soybean disease in the US. The nematode is near our borders and is expected to appear in the state at any time. As yet there has not been a confirmed report of SCN in the state.
Berlin Nelson, Plant Pathologist
Carl Bradley, Extension Plant Pathologist
Department of Plant Pathology, NDSU