In our forage crops, we started with bad stands from dry weather at planting . Cold weather in early November and after Christmas has not helped in growth rate. Barley Yellow Dwarf Virus is vectored by aphids and could also be causing some of our issues. UGA Extension Forage Scientist Dr. Dennis Hancock says reports of BYD are coming in from South GA.
In some oats, I noticed an abundance of aphids last week. We’re used to counting aphids for grain crops, but we have to also think about forage crop management too. BYDV can severely damage wheat and barley, but oats are more susceptible. UGA Extension Grain Entomologist Dr. David Buntin says, “The best treatment time usually is at full-tiller stage in early to mid-February. But, scout fields for aphids at 25 – 35 days after planting and during warm periods in January.” Especially if these fields were planted earlier, which Dr. Buntin says is more likely to get BYD. Could we may be seeing issues with BYDV earlier than normal? Something we need to keep in mind.
Also, oats are also more susceptible to cold, and nutrient symptoms may look similar to BYD. When we have cooler temperatures, this slows P movement into the root and we’ll see a purplish color which is textbook phosphorus deficiency. Plant roots have to be in direct contact with P for uptake. This is called “root interception.” Cold temperatures slow the growth of roots and we see this deficiency. Nutrient take up is different in nitrogen, called “mass flow”. This is because N is mostly taken up as nitrate in water.
The virus is present in most fields throughout the winter and once we get it, there is nothing that can be done. Here is an excerpt from Dr. Buntin about management of BYD:
“Systemic seed treatments, imidacloprid, thiamethoxam, and clothianidin, are available for controlling aphids in the fall and winter and may reduce infection rates of BYD. These seed treatments are more effective in the northern half of the seed treatments have been inconsistent in control and are not recommended for routine use. A single, well-timed insecticide application of the insecticide lambda cyhalothrin, or gamma cyhalothrin also can control aphids, reduce the incidence of BYD and increase yields… A lambda cyhalothrin or gamma cyhalothrin treatment at full tiller can be applied with top-dress nitrogen. OP insecticides, such as dimethoate and methyl parathion, also will control aphids but are not effective in preventing barley yellow dwarf infection.
Planting date is the single most important management practice, with early plantings generally have greater aphid numbers and greater BYD incidence than late plantings.”