ISSUE 14 August 4, 2005
NDSU IPM SURVEY, JULY 25-29
NDSU IPM field scouts are winding up surveys of small grains during the first week of August in most of North Dakota, as much of the crop is maturing and disease evaluations can no longer be made. Field scouts will concentrate on soybeans, sunflower and canola post harvest evaluations in the next few weeks.
Wheat: During the last week of July, NDSU IPM scouts surveyed 117 wheat fields across their scouting regions. In non-mature fields, scouts were still observing abundant infections of leaf rust, tan spot, Septoria, and in some cases bacterial stripe. Barley yellow dwarf symptoms were common in some wheat fields in the central and east central counties. Head diseases also became more apparent.
Symptoms of Fusarium head blight, or scab, was observed in 71% of the fields surveyed during the last week of July. Field severity or index (% tillers infected x average % head severity) ranged from <1% to 58.5% in fields showing symptoms (see figure below).
The highest severities were observed in the eastern part of the state, with low to no scab observed in the southwest. Average field severity index across infected fields was 10.7%.
Ergot infections were observed in 15% of scouted wheat fields, and loose smut was observed in 10% of scouted fields. Ergot infections are favored by wet weather at flowering, while the loose smut infections were seed borne and present at the time of planting.
Barley: Only 13 barley fields were surveyed during this last week of July, as most barley fields are now mature. Barley leaf rust was observed in 11 of the 13 fields, and leaf spot diseases also were common. Most of the barley fields surveyed were in the southwest, and none showed scab symptoms. Ergot infections were observed in 4 of the 13 barley fields surveyed.
Soybeans: The NDSU scouts surveyed 41 soybean fields the last week of July. Of these, 85% had soybean aphids present, but none had reached the economic threshold of 250 aphids/plant for treatment.
Sunflower: Fields scouts examined 24 sunflower fields and 10 of these had downy mildew symptoms, ranging <1% incidence to 17.5% incidence. Field scouts also were detecting sunflower beetle larvae and sunflower seed weevils at this time.
QUESTIONS ABOUT SCAB AND VARIETY RESPONSE AND FUNGICIDE RESPONSE
A considerable amount of information will be gathered this year on variety response to Fusarium head blight (scab) infections across North Dakota, South Dakota and Minnesota. Farmers will have their own experiences with varieties and also fungicides, but may not have adequate comparisons to evaluate other varieties or treatments, or how things performed under different conditions.
The extent of diseases this year across multiple research locations will allow extensive gathering of data on differences among varieties and fungicide treatments. Disease observations have been taken at many of these plots, both at the research extension centers and at off-station sites. The next piece of information about variety and fungicide response will come from harvest data, and harvesting is just beginning at some locations. Data on DON (vomitoxin) levels will be the last piece of information gathered, as most grain from research plots will be sent to the NDSU Veterinary Toxicology Laboratory for analysis.
Once the data has been compiled and analyzed, we should have excellent information to provide to growers for their consideration. We put a lot of value in these plots because we have replicated data at each site, but also because we will have multiple locations across the region that will have disease information. Stay tuned for this information as it becomes available later this month and into early fall.
NDSU Extension Plant Pathologist
NDSU PLANT DIAGNOSTIC LAB
Sugar Beet Virus Testing. The NDSU Plant Diagnostic Lab can now test for Beet Soilborne Mosaic Virus (BSBMV). If symptomatic roots are submitted to the lab, results can usually be obtained within 2 days, since no culturing is needed. As in previous years, the NDSU Plant Diagnostic Lab can also test for the Beet Necrotic Yellow Vein virus (causal agent of Rhizomania). Samples should include several roots (foliage isnít needed), and if you plan on shipping them, wrap roots in dry paper towels before placing in plastic bags. Regular mail usually suffices to get samples to the lab within 24 hours, but please avoid shipping on a Friday. A hot post office over the weekend can lead to a soupy surprise by Monday.
Tomatoes Ė Nitrogen excess. Excess nitrogen on tomatoes can result in beautiful vegetative growth, but few flowers and fruits may develop. If you seem to be waiting unreasonably long for the first red-ripe tomato of the season, remember this for next year and try using either less manure or a complete fertilizer with a higher phosphorus content, such as a 5:10:10 formulation or a 8:16:16 formulation. Generally, a 2-3 lb per 100-sq.ft application of complete fertilizer is sufficient. If you think you may have applied too much nitrogen, try inducing a little stress into the plant, by, for example, withholding water. A little water stress might promote faster ripening of the fruit, but this doesnít necessarily work all the time. Otherwise, nothing can really be done about this problem, except to hope for a long growing season.
Tomatoes Ė Blossom end rot. Some tomato enthusiasts may on occasion notice a disorder known as blossom end rot. The symptoms of blossom end rot include a dark brown or brownish black, sunken, distinct lesion or blotch on the bottom (blossom end) of the developing fruit. This disorder has been attributed to a calcium deficiency, which seems counterintuitive if your soil is high in calcium, like the test plots in Idaho where I would see this disorder almost every year. Like some other deficiencies, itís not necessarily low soil levels of the nutrient that cause the problem. Instead, the soil may have plenty of a particular nutrient, but the nutrient might not be accessible by the plant, which was probably the case in my Idaho tomato trials. Wide swings in soil moisture and excess nitrogen have also been associated with blossom end rot. In situations where excess nitrogen may play a role, the thought is that calcium is diverted from developing fruit to new foliar growth. Certain Roma varieties seem to be more susceptible to this disorder than other tomato types.
The bad news is that affected fruit cannot be cured. The good news is that the amount of affected new fruit might be reduced if a foliar application of calcium chloride is made. I have no personal experience with this remedy, but it may be worth a try if you have a particularly severe problem with blossom end rot. Of course, carefully read the label for this product, since an excessive application may burn foliage. Affected fruit can still be eaten, after removal of unsightly affected portion of fruit. Some practices that may help reduce this problem in next yearís garden include using varieties that are more tolerant of this disorder, maintain even soil moisture to avoid extreme fluctuations between wet and dry (use of mulches can help), and avoid applying excess nitrogen.
The anticipation for those first fruits can almost be unbearable. And if you are struggling with excess nitrogen problems or blossom end rot, hope for the best, but also consider making good friends with a neighbor who may be having better luck this year!
Plant Pest Diagnostician