ISSUE 11 July 13, 2005
NDSU IPM SURVEY, JULY 5 - JULY 8
NDSU IPM field scouts surveyed 105 wheat fields and 22 barley fields the first week of July. The wheat crop growth stage ranged from jointing (primarily in west central and northwest districts, to early dough stages along the southern counties. In wheat, field scouts observed wheat leaf rust in over 35% of the fields surveyed, with flag leaf severity ranging from 1% to 90% in some winter wheat (see leaf rust flag leaf severity map).
Wheat tan spot was also common and severe in some fields (see tan spot flag leaf severity map).
Head scab was observed in 22.8% of the wheat fields severity, with field severities (incidence of tillers infected x head severity) ranging from less than 1% to over 25% in some winter wheat fields. Head scab was primarily observed in counties in the southcentral and southeast districts (see wheat head scab map).
Loose smut was observed in 19% of the surveyed wheat fields, with incidences of infected tillers generally between 2 and 6%, but a few fields had 20 and 26% infected tillers.
In barley, leaf spot diseases of spot blotch and net blotch are very common, but generally not yet severe on the flag leaf. Barley leaf rust also was detected in three barley fields surveyed, and head scab was observed in one barley field. Barley crop growth stages ranged from jointing to dough stage.
WINTER WHEAT AND HEAD SCAB
Winter wheat plots near Ellendale and Lisbon have severe infections of head scab (Fusarium head blight). Commercial winter wheat fields in southeast and east central counties also show some severe infections. I evaluated the winter wheat plots at Ellendale for disease levels on June 7th. Winter wheat varieties at the Lisbon site are being evaluated on July 12th.
At the Ellendale site, the scab field severity (incidence of tillers infected x average head severity) was extremely high for the variety Jagalene (94%), followed by Wesley (69.4%), Falcon (65.8%), Expedition (46%), Millennium (45%), Jerry (35%), and Harding (32%).
Fungicide treatment of these varieties at flowering did result in reduction of head scab, a reduction of about 43% in Jagalene and Wesley to a 76% reduction in Harding. Unfortunately, in very susceptible varieties such as Jagalene and Wesley, fungicide reductions of head scab at 43% arenít going to be enough to result in satisfactory yield or quality. Fungicide treatment resulted in almost complete control of leaf rust and 90% control of fungal leaf spots. Flag leaves in untreated plots were essentially dead.
Much of the winter wheat in the southeast and south central areas of the state flowered during a very rainy period, between June 13 and June 22. Dewpoints also were very high from June 18 to June 23. So conditions were favorable for infection at that time, and rains previous to flowering were favorable for the fungus to develop spores. Similar conditions have existed in many areas during spring wheat flowering, but the resistance level of many spring wheat varieties is higher than that found in winter wheat, and recent hot temperatures may help shut down spread of scab in spring wheat.
SECTION 18 FOR QUADRIS APPROVED ON SAFFLOWER
A section 18 emergency exemption for Quadris to be applied on safflower for Alternaria leaf spot control was approved last week. The exemption is effective from July 6 to Aug. 15, 2005. According to the use directions, a single application of Quadris may be made by air or ground at a rate of 6.2 to 9.3 fl oz/A. The application should be made at the onset of the first flower ray on the primary head on the first plant in the field. The use directions are posted on the NDSU Extension Pesticide Program and the ND Department of Agriculture websites at:
Carl A. Bradley
Extension Plant Pathologist
NDSU PLANT DIAGNOSTIC LAB
The bulk of samples received by the NDSU Plant Diagnostic Lab continues to be dominated by sunflower, sugarbeet, and soybean. Dry bean and corn samples comprise an important, though relatively small, proportion of samples received. Flax, canola, and alfalfa are an even smaller component of samples received lately. Wheat and other small grains, though dominant in May, were rarely submitted in the past few weeks, as these crops approach (or have approached) maturity.
Symptoms observed on recent samples include poor growth (both foliar and root), iron chlorosis, those that resemble growth regulator herbicide injury (especially in soybean and sunflower), and root rots. Early Septoria brown spot, a relatively minor problem on soybean, was observed on a few soybean samples. Root rots were detected on soybean, dry bean, and sugarbeet, and causal agents included Aphanomyces (sugarbeet), probable Rhizoctonia, and, of course, various Fusarium species.
Fusarium species can be detected in nearly all samples that exhibit decayed plant material, and they are not always the cause of the problem. Knowing the actual Fusarium species is important when determining a crop rotation, because not all Fusarium species affect crops equally, and some may be solely saprophytic. The lab can, to a very limited extent, attempt to speciate Fusarium. If you are interested in this type of service, please contact the lab for more information. Speciation is a very time-consuming process, so results may not be obtained for several weeks to several months. And, depending on the skill of the person making the identification, a precise identification may not be possible without further testing and additional time.
Several ornamental crops have also been submitted, and the predominant problems were various fungal leaf spots and insect injury. One particular insect that has been noted around Fargo is the cottony maple scale. This scale is usually not noticeable on the host (maple trees, particularly silver maples), because the female is brown and flat. The critters mate in fall, and the females overwinter on the twigs and stems in their flat, brown state. In spring, a cottony egg sac is visible on the posterior of the now-noticeable expanded females, and, to quote the Insect and Disease Management Guide for Woody Plants in North Dakota, "heavily infested branches with white egg sacs look like they have been strung with popcorn." For more information, follow the link below: