Friday, August 2, 2013

Crop Alert: June 26, 2013

This Crop Alert was originally written for and distributed to farmers and other members of the agricultural industry in western New York.

By Bill Verbeten & Mike Stanyard, Cornell Cooperative Extension

Potato Leafhoppers
This yearly alfalfa pest has arrived across western New York on the storms we’ve had in recent weeks. Reports of leafhoppers over threshold are coming in from across the region, however many fields won’t be sprayed because second harvest will occur soon after this latest round of rain on many farms. If first harvest was delayed and 2nd harvest is more than a week away it will be very important to get out in the fields and scout for leafhoppers once it dries out. The re-growth after 2nd cut will also need to be watched closely while it’s small to keep the leafhoppers in check. For more discussion on this topic see Mike’s June 2006 Ag Focus article.

Yellow Soybeans
The soybean fields that have managed to survive the floods have been looking pretty yellow in parts of western New York. In addition to being a bit waterlogged, the soybeans are currently transitioning from their using the energy in their cotyledons for growth to relying on photosynthesis. Furthermore the soybeans are probably just being to form nodules and fix nitrogen, see this video from the University of Wisconsin on the topic of yellow soybeans.

Septoria Brown Spot
We are starting to see some brown lesions on the lower leaves of soybean plants. Septoria brown spot is probably the most common early leaf disease that occurs with wet warm weather, Figure 1. This fungus will start on the unifoliate leaves but can spread upward to the trifoliates. Soybean plants usually can outgrow it and the lower affected leaves will yellow and fall off. Usually not yield limiting unless it spreads to upper trifoliates on small plants.

Figure 1: Septoria Brown Spot on Soybeans

Side-dressing Corn
The rains have washed away much of the nitrogen put down at planting with the corn. Pre-sidedress nitrogen test (PSNT) samples from across the region have come back very low in a number of cases (below 10 PPM). If you take PSNT samples and they come back ≥ 25 PPM (not very likely this year) no side-dress nitrogen is needed. PSNTs between 21-24 PPM should have 50 lbs. N/acre this year with all of the rain (in dryer years 25 lbs. N/acre would be more appropriate). Below 21 PPM (very common this year) higher rates of 75-150 lbs. N/acre are justified. For a recommendation more tailored to your farm see the Cornell Corn N Calculator. For more information on PSNT sampling and recommendations see the Cornell PSNT Factsheet.

When side-dressing nitrogen, it should be injected/knifed in if possible. Dribbling liquid nitrogen on will have lower losses than broadcasting, but more than injecting. Adding a nitrogen stabilizer to side-dress fertilizer will not be worthwhile.

Fusarium head blight update, June 28, 2013
from Gary Bergstrom, Extension Plant Pathologist, Cornell University

Winter wheat in New York flowered primarily at the end of May and first few days of June during a period when the Risk Assessment Tool indicated low risk of FHB. Field observations this week in scattered locations across New York are telling a somewhat different tale. Some level of FHB is now visible in most winter wheat fields in the state, some non-sprayed fields in the range of 5-10% incidence. Even if you checked your fields a week ago, I urge you to check them again as symptom development has increased following the shift from cool to warmer temperatures. If you see significant incidence of FHB you might consider having a pre-harvest test done for DON toxin contamination before shipping your wheat to a flour mill. Much of the small, scattered acreage of spring wheat and barley flowered over the past week or so when the forecast risk of FHB was moderate to severe. Growers can still make an application of Caramba or Prosaro if the spring crop is within 5 days of the start of flowering (first yellow anthers appeared). Most are past that time. FHB symptoms should start to appear in the next week or so; with the high risk of the past two weeks, monitoring of spring grains will be very important this year. Powdery mildew, Stagonospora nodorum blotch, and leaf rust development has been observed on flag leaves of winter wheat; flowering sprays with Caramba or Prosaro appear to have reduced the severity of flag leaf disease to a significant extent. Stripe rust of wheat has been observed at low levels in Tompkins and Monroe Counties and was also recently reported in Grand Isle County, Vermont.

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