Roundup of crop conditions, weather trends and outlook and additional categorical updates, as the growing season progresses.

Crops

Corn and soybeans continue to progress and look good throughout the region, where timely rainfall has occurred. The earliest corn fields have reached the blister stage (R2) while later-planted fields are still pre-tassel.

Soybeans are straddling full flower (R2, open flower at one of the two uppermost nodes) and beginning pod (R3, 3/16 inch or longer appear at one of the four uppermost nodes) in most fields although earlier-maturing fields have reached R3 already.

When staging reproductive-stage soybean, begin counting the nodes starting with the first mature trifoliate, i.e. the one just below the newest trifoliate with leaf edges no longer touching. Canopy closure has occurred in most fields which will keep the crop below the canopy humid and moist longer each morning. This will increase the risk of disease, but will  help to ensure that spider mites do not erupt with hot weather on the way.

Weather

Temperature range during the last week of July was 2 to 4 degrees above normal on average in the southern tier of counties and considerably warmer than that in eastern Michigan. We picked up 218 growing degree days (GDD, base 40 for alfalfa) or 148 GDD50 (for corn and soybeans) last week.

The forecasted reference evapotranspiration (FRET) rate was 1.4-1.5 inches for the week ending August 5. The forecast eerily predicts the addition of the same number of GDD’s—218 GDD40 or 148 GDD50—in the coming week. There is high confidence in both the 6-10 day and 8-14 day outlooks for above-normal temperatures during the first half of August.

Precipitation was meager during the last week of July with less than a tenth of an inch for most of us. Most of the region was wetter than normal over the entire month of July with rainfall totals of 0.5 inch to as much as 4 inches more than normal.

Medium-range outlook calls for slightly below-average chance of precipitation during the first half of August.

Disease

Tar spot in corn has been confirmed only in Lenawee County so far this year, and risk is medium to high in St. Joseph, Branch and Hillsdale counties, according to the Tarspotter app. As heavy morning dew and foggy weather become more common in August, the risk for the disease will increase. Soybean foliar diseases have begun to show in some fields with more dense canopies. Frogeye leaf spot, Septoria brown spot and possibly early signs of SDS have been found. Scouting prior to R3 will help to determine which fungicides are needed to control existing diseases and those that historically are a problem in a given field.

An interesting wheat disease call came associated with a recently harvested field. The heads in large sections of the field were black which is a common symptom of sooty molds that are caused by a number of opportunistic saprophytic fungi. Though the disease does not usually infect kernels or impact yield, or produce toxins, this field experienced severe kernel degradation and reduced yield. If you suspect a disease in your wheat field, we encourage you to collect samples of the affected plants and send them to the MSU Plant & Pest Diagnostics lab — the Michigan Wheat Program covers the cost of the lab analysis.

Irrigation

Corn from V16 through beginning dent has a Kc of 1.2 and will require 1.5-1.7 inches this week. Soybeans at R2 (full bloom, Kc=1.1) will use 1.4-1.5 inches, and early fields that have reached R3 (beginning pod, Kc=1.2) will use 1.5-1.7 inches.

Pests, insects

Western bean cutworm moth trap counts held steady in some traps and dropped off in others last week. However, traps in central Michigan are reporting trap counts of 200-300, likely due to the storms that came through that region on July 23rd that largely missed our region. Trap counts in northern Indiana were hit-or-miss with some increasing over the previous week while others held steady or dropped off. Overall, counts throughout Indiana either remained low or decreased, so it appears that the peak flight time for WBC to our south was during the week of July 14-20 this year while peak flight in southern Michigan was over a wider range between July 6-19. No fall armyworm moths were captured last week, but heading into August is when we would expect to see an increase in activity.

Insect identification and management was the topic of last week’s MSU Extension Field Crops Virtual Breakfast with field crop entomologist Chris DiFonzo. There are no major insect concerns currently, so she took the opportunity to discuss how to identify several species and some of the main scouting and management highlights of each. Identifying insects is important for many reasons, including being able to select an effective insecticide but also knowing which insects are problematic along with their treatment thresholds as well as which insects are beneficial.

Western bean cutworm scouting is important with fields that are at different growth stages than those in the vicinity as females will target pre-tassel fields to lay eggs. A later-planted field may end up being a “trap crop” for this species. Moth trap counts are not an indicator of intensity of infestation potential in corn as they are with dry beans, but they help to know when peak flight times occur. After the female moths lay eggs (generally on the ear leaf or 1-2 leaves higher), the eggs will change color from white to brown to dark purple/black as the larvae develop.

The management threshold is 5% of plants with an egg mass, and this number is cumulative. In other words, if you scout 100 plants in a field this week and find 3 egg masses, then find another 3 egg masses out of 100 plants next week, you have reached the threshold for that field.

The eggs you saw last week will have hatched in 5-7 days, so scouting every seven days will ensure you are not double-counting.

DiFonzo stresses that when tank mixing an insecticide with a fungicide, time the application that makes the most sense for the fungicide as insecticides are typically cheaper and the timing a bit more forgiving.

This article originally appeared on Sturgis Journal: News