Crop & Pest Report - All
Soybean Aphid Continues to be Low
About 135 fields were scouted by the NDSU and UMN Crop IPM Scouts for soybean aphids the last two weeks. Overall, soybean aphid populations continue to be low and below the economic threshold (average of 250 aphids per plants on 80% of the plants and increasing populations). This is probably due to several factors: 1) severe thunder storms washing aphids off plants; 2) beneficial fungi that infect and kill aphids (Moist, humid environments in the soybean canopy favor development of fungal infections.); and 3) hot temperatures above 90F slow soybean aphid growth and reproduction.
The percentage of plant infested by soybean aphids has been increasing in northern RRV, Fergus Falls area, and southwest Minnesota. The IPM crop scouts in North Dakota and Minnesota found soybean aphids in 40% of the soybean fields surveyed (last week was 26%). Percentage of plants infested with soybean aphids ranged from 0 to 90% with an average of 26% of plants infested. Last week’s incidence report was 0 to 77% with an average of 14% plants infested. The average number of soybean aphids per plant ranged from 0 to 29, and increased from last week’s scouting report of 0-10 aphid per plant. We are still below the economic threshold; so, scouting is critical for the next several weeks with slowly increasing soybean aphid counts.
Continue to scouting through R5 (beginning seed). The USDA NASS reports that 81% of the soybeans were blooming (R1), and 36% setting pods in North Dakota (USDA NASS News Release – July 24, 2016).
Alfalfa Webworm in Soybeans and Sunflowers
Alfalfa webworm larvae (worms) have been observed causing foliar defoliation in soybeans and sunflower, mainly in the north central area of North Dakota. Some of the field reports include Makoti, Minot, Mohall and Max.
Alfalfa webworm larvae are 1-inch long when mature. They are greenish to nearly black with a light stripe that runs down the middle of the back. These larvae feed for about 3+ weeks. Scouts often observed the light webbing over the leaves and frass (black fecal pellets) made by alfalfa webworm larvae first. These larvae move very rapidly, forward or backward, when disturbed.
All foliage-feeding caterpillars present in a field are grouped together for determining if fields are at the economic threshold (E.T.). For sunflower, use 25-30% defoliation as the E.T. For soybean, the E.T. is based on crop stage and foliar defoliation (see foliar defoliation guide). Moderate defoliation early in the season has little effect on final soybean yield. As soybeans reach the flowering and pod filling stages, then defoliation poses a greater threat to yield. Use the following E.T. for foliage-feeding caterpillars in soybeans:
- Flowering - 40% defoliation
- Bloom-pod - 20% defoliation
- Pod fill-harvest - 35% defoliation.
Although some of the warmest temperatures of the summer have been recorded in the past couple of days and today, and for some locations even Friday having 90° plus potential, the general trend this coming week will be for cooler rather than warmer temperatures. This transition to cooler temperatures will have two noticeable impacts. The first will be a high likeihood of thunderstorms, probably widespread over much of North Dakota on Friday into Saturday. After that system exits, cooler and drier air will move into the northern plains. That will bring the second notable feature of the next seven days; fewer hours with high relative humidity (Figure 1). It appears that most locations will record between 10-20 fewer hours where relative humidity values are above 85% during this period than were recorded during the past week.
Even with a transition to cooler, but far from cool, temperatures, the number of growing degrees days (GDDs) are expected to be greater than in the past week (Figure 2). Although it has been quite warm these past couple of days, it was cool of course for several days before this brief “heat wave” started. Therefore, expected GDDs this week will be slightly higher than the previous seven days, plus, once we get into this weekend and into next week, the temperatures will be at a more optimal level for good plant development without worries of heat stress. It appears that minimums will mostly be around 60° or in the 60s with maximums in the low to middle 80s.
Beyond this seven day period, current indications are that temperatures near normal, or even slightly below normal, will continue through the first part of August. This period of “normal” temperatures looks to be occurring not only in our region, but throughout much of the north central part of the lower 48 states, including Iowa, Illinois and Indiana. Higher heat will likely return in August, but the next 10 days does not show any signs of high heat returning once we get through this weekend.
(701-231-8209) Twitter: @darylritchison
Harvest has begun in pea and winter wheat fields. Some are still working on their first cutting of hay, it is not only hay ground that is being baled as some hail damaged and droughted grain fields are being baled. Some rain fell in the last week. NDAWN recorded 0.20 inch in Dickinson between July 12th and July 19th. High temperatures are forecasted and with the heat, be sure to be well hydrated and stay safe.
On July 13th we had our agronomy field day in Dickinson. Topics covered were tile drainage, seeding rates, weed control, disease management, and marketing.
Area Extension Specialist/Cropping Systems
NDSU Dickinson Research Extension Center
Based on NDAWN, the region’s rainfall during July 12-18 ranged from none (several locations) to 0.5 inch (Oakes). Daily water use by corn is ranging from 0.25-0.33 inch. Corn planted April 29 has accumulated 1040 to 1340 growing degree day units through July 18.
Harvest is beginning for winter cereals, barley and field pea. Spring wheat is physiological mature. Corn is in the VT (tassel) to silk (R1) stages. Soybean is in the full flower to initial pod-development (R2-3 stages). Dry bean are flowering and sunflower are nearing this stage (R5). Harvest continues of grass hay and second cutting of alfalfa. Bacterial disease is appearing in dry bean with recent heavy rain, wind and spotty hail.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center
Hit and miss rain chances have continued throughout parts of North Central North Dakota over the previous week: Minot: 1.04”, Rugby: 1.27”, Berthold: 1.08”, Bottineau 1.08”, and Mohall: 0.30” (July 11th – July 19th).
As winter wheat harvest approaches, consider your plan in Wheat Streak Mosaic Virus (WSMV) management. Destroy volunteer small grains, grass weeds, and other WSMV hosts at least two weeks prior to seeding winter wheat. Always avoid wheat-on-wheat rotation to help break the green bridge to help limit the movement of wheat curl mite (Aceria tosichella Keifer).
Pea Aphid “hot spots” have been found in Ward County. Continue scouting protocols to monitor thresholds. If economic thresholds are met, consider the stage of your crop to determine if chemical treatment is warranted. Refer to the NDSU North Dakota Field Crop Insect Management Guide (E-1143) for threshold and treatment recommendations or reach out to me at the NCREC to discuss field observations and possible plans of action.
Yesterday (July 20), growers were welcomed to the North Central Research Extension Center near Minot to attend the 2016 Field Day focusing on “Improving Efficiencies of Spring Wheat Production.” Attendees were updated on several topics including, but not limited to, pesticides, cover crops and saline soils, and a pest clinic. Furthermore, field days will take place in Renville County on July 21st and Pierce County on July 22nd. We hope you can join us!
Area Extension Specialist/Crop Protection
NDSU North Central Research Extension Center
New Pollinator Bee Gardening Extension Fact Sheet Available
H1811 Bee-utiful Landscapes: Building a Pollinator Garden is now available from the NDSU Distribution Center or you can download the publication as a pdf from their website. Both native bees and European honey bees are in trouble in the United States. Homeowners can have a major impact on pollinators by planting a pollinator garden and providing suitable habitat. This publication will help you identify major pollinators, choose plants that will provide a continuous source of nectar and pollen, and safely use pesticides.
Herbicides Safe to Cover Crops
Question: Had a customer inform me this morning he is setting up a Valmar system on his side dress fertilizer rig so he can broadcast his cover crop mix while side dress application in corn. Is there a cheat sheet yet for what I can recommend for herbicides when considering there will be seeding of cover crop approximately 30 days later?
Answer (including comments from Dr. Abbey Wick): This is where weed science is lacking in information. We have started to build a guide to herbicide residue and fall cover crop establishment on page 105 in the NDSU weed guide, and we will build on it as we get more information. Also, a guide from the University of Wisconsin is a good place to start. If you click on the link on that webpage it should bring up the circular.
Lee Briese (ND consultant) has produced an excellent resource of genus and species of cover crops so that it can be compared to the different crops in the weed guide to estimate rotation intervals.
Greg LaPlante (ND Consultant) identified another resource from the University of MN:
Extension Weed Specialist
Protect Bees from Pesticide Poisoning
If you need to spray flowering sunflowers or other flowering field crops, please remember to PROTECT BEES by notifying bee keepers before an insecticide application (at least 1 day notice if possible), using least toxic insecticide products to bees, and spraying in late evening.
To find bee keepers, see the North Dakota Bee Map on the North Dakota Department of Agriculture website and zoom in on the area of interest to find names and contact information of bee keepers. An NDSU YouTube video is available on Protect Bees from Pesticide Poisoning. Always read, follow and understand the label in regards to pollinator protection.
Research Specialist & IPM Coordinator, Extension Entomology
Weather/Crop Phenology Maps
Professor of Climatological Practices