|Corn and soybean issues|
|Thursday, June 06, 2013 12:22 AM|
BY JAMES HOORMAN
OSU-Extension- Putnam County
The recent rains have blessed our farms; but look out for diseases, insects, and replanting if necessary. The cool temperatures and low rainfall has depressed most wheat diseases until this past weekend’s rains occurred.
Paul and Salgado, CORN Newsletter, 2013 state “While most wheat should have flowered this week, there is considerable variation in crop development and late-flowering fields are at risk for head scab. Cool conditions can extend the wheat flowering window beyond the 2-3 days that is typical under warmer conditions, putting some fields at risk for scab. Producers with wheat flowering this week consider applying Prosaro or Caramba if the risk for scab increases.”
Also, Paul (CORN newsletter, 2013) notes “Unseasonably cold temperatures in May have some producers concerned about wheat frost damage. Some areas recorded temperatures as low as 30-35F and a few frost-damaged spikes are showing up. Wheat is most sensitive to frost damage during the heading and flowering growth stages, since freezing temperatures at these stages may lead to sterility. Pollination wheat flowers and developing grain are less sensitive to cold temperatures and should be safe. Open a few florets at several locations across the field and examine the grain. Healthy, greenish-white, developing grain is a good sign. Injured kernels are usually shriveled and whitish-gray in color. Frost damage tends to be most severe when flowering-heads are exposed to temperatures of 30F or below for at least two hours.”
There are several insects to watch out for in hay, corn and soybean fields. In hay fields, alfalfa weevils are common but if you have not made your first cutting yet, making hay is the best option for control. Check for larva feeding on regrowth and apply an insecticide treatment if necessary. In corn, black cutworm may be a problem in weedy or no-till fields with lots of vegetation or residue. Small corn that is late planted is more susceptible to black cutworm larva feeding (Hammond and Michel, 2013, CORN newsletter).
Farmers are reporting adult black flies with long wings in large numbers in both corn and soybean fields which are probably adult seedcorn maggots. They prefer cool wet weather and lots of organic residue or weedy fields. The seedcorn maggot can develop in 21 days and they can be a problem until mid-June. The seedcorn maggot is described as a small, yellowish white larva that feeds on germinating seeds on both corn and soybeans. Reduced stands and slow emerging crops are a sign that seedcorn maggots may be present along with grubs and wireworms. Seed corn maggot may be found over large areas of a field while wireworms and grubs are more localized problems and replanting may be necessary. Use a good insecticide treatment to manage this problem during replanting. (Food Safety Network, 2001)
For replanting soybeans, the Ohio Agronomy Guide, 14th edition says an ideal planting density is 3 to 3.3 seeds per foot on 7.5 inch drilled rows of soybeans. They do not recommend replanting or interseeding unless you have less than 1.5 healthy plants per foot of 7.5 inch drilled soybeans.
For corn replant, the Agronomy Guide says 10-15 percent loss of seed is common. Typical seeding rates are 30,000 to 32,000 seeds per acre or slightly higher. Corn planted June 3 at 30,000 seeds per acre can achieve about 80 percent of normal yields. An existing corn population of 15,000 plants planted before May 9 still has a harvest potential of 79 percent of optimal yield or 1 percent (80-79 percent) yield difference.
Thomison (CORN newsletter 2013) says “Replant decisions in corn should cover replant costs plus make it worth the effort. Add a 5 percent yield loss penalty for gaps of 4-6 feet within rows and a 2 percent yield loss penalty for gaps of 1-3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. Corn yields are reduced by more numerous and longer gaps between corn plants.”
If in this example you gained 1 percent from the difference in planting date plus 5 percent yield loss for 4-6 feet gaps, this equals a 6 percent yield difference. A normal corn yield is 180 bushel times 80 percent or 144 expected bushel times the 6 percent yield difference equals 8.64 bushels. You have to decide if 8.64 bushels corn is worth enough for you to replant. Generally farmers only replant the worst portions of their field where few plants are growing. Check the Ohio Agronomy Guide for more details.