The upcoming weekend rainfall (our meteorologists seem assured that it’ll be widespread) should greatly help parts of Virginia that are short on or getting short of topsoil moisture and position us perfectly for a good start to the soybean growing season.
However, with the rainfall comes cooler soil temperatures. Below are predictions for 4-inch soil moisture and soil temperature over the next 10 days from Orange (one of the coolest parts of Virginia) and Suffolk (one of the warmest parts). As you see, soil temperatures will plummet from relatively warm (>60o) to nearly 50o or less over the weekend. While soybean seed will germinate and emerge in a reasonable amount of time at 60O, germination and emergence will be very slow when temperatures dip below this.
Therefore, heed my suggestion and make sure that you have a good fungicide seed treatment on anything that you are planting now or early next week.
Below is the fungicide efficacy chart from our Pest Management Guide. The main diseases that we need to concern ourselves with are Rhizoctonia and Fusarium sp. If in wet soils, Pythium and Phytophtora sp. could also be a problem with slow-emerging soybean. Be sure to protect a slow-emerging crop with a fungicide containing the active ingredients that provide good to excellent control of the appropriate disease.
It looks as if we have come out of the unusually warm pattern we experienced during late-March thru early-April and fallen back into a cooler one. I’ve watched unusually warm soil temperatures fall rapidly during that period. Although long-term weather forecasts are speculative, it appears that the next week or so will be cooler-than-average. Below are the GFS (U.S.) and European model predictions thru next Thursday. Although today (Thursday) is very warm (& wet), notice that both models are showing below-average temperatures.
These low temperatures are also predicted to persist thru mid-May, as shown below.
Keep in mind that the predictability of these models are quite low past 1 week, so this could change substantially. Still, we are dealing with some relatively cool soils and that need to affect our planting decisions once things dry up.
When soils are cool, we must get the plants up and out of the ground as soon as possible. The longer a sprouted seed is in the ground, the more likely it will be infected with numerous seedling diseases. We must always strive for rapid emergence.
Before we get into too big of a hurry to plant, we must recognize that yields will not decrease drastically for over a month. Although the date when such a decline takes place will vary with the year, my data and experience indicates that this date will not occur to the first week of June. Depending on the number of acres you need to plant, you may not need to get in that big of a hurry. If the same 2-week pattern of cold then warm periods continue, I expect to see a warm-up and warmer soils by the second week of May.
If you must plant into cool soils, I suggest that you use fungicide-treated soybean seed. This will provide some protection if the seed does remain in the soil for an extended period. Below is a table that Dr. Hillary Mehl used this winter listing the effectiveness of several active ingredients with diseases that commonly occur in Virginia. Rhizoctonia and Fusarium have traditionally been our most troublesome. Pythium can also raise it’s head occasionally. Note that only one of these treatments listed are good on sudden death syndrome (SDS), but there is now at least one other product available . I caution that nematodes are often involved with SDS, so additional measures will likely be needed to fully manage that disease.
Finally, don’t plant the seed too deep. 3/4 to 1 inch deep is enough. Planting deeper will delay emergence.
We were hoping to be about half way finished with our soybean plantings by now, but we haven’t put a planter in the field in two weeks. The rain continues to delay us, but I hope that we will get back into the field next week.
The rain and cooler weather has lowered soil temperatures somewhat and this means that we need to take a few extra precautions, especially pertaining to seedling disease. I wrote a detailed blog a few years ago on seedling disease; little has changed and, for more details, you can view that blog here:
Planting soybean in cool soil will lead to delayed emergence and increased chance of seedling disease that can reduce stands, weaken emerged plants, and inhibit early-season growth. I stress that the greater time required for emergence, the greater probability that the seed will become infected with soil-borne disease. If you are planting into cool soils, I strongly suggest using fungicide-treated seed as an insurance against seedling disease. These treatments will protect the seed and seedling if emergence is delayed.
But, seed treatments should not be a substitute for other practices that encourage rapid seedling emergence. Here is my checklist for insuring a good stand free of seedling disease:
Know the germination and vigor of your seed; adjust the seeding rate accordingly.
Insure good soil-to-seed contact by properly setting your planter to cut through the residue and penetrate to the proper depth.
Plant soybean seed ¾ to 1 inch deep into good soil moisture. Planting deeper will delay emergence
Consider fungicide seed treatments if planting into cool soils.