Aphids and Barley Yellow Dwarf Virus
Posted: April 23, 2013
One of the key pests of small grains, timothy, and other grass crops are cereal aphids, which comprise many aphid species including bird-cherry oat aphid, corn leaf aphid, English grain aphid and greenbug. Most of these aphid species usually do not inflict economic damage by themselves, particularly in spring when natural-enemy communities can keep their populations in check. Greenbug is an exception however because they feed by injecting toxic saliva into plants causing yellowing that resembles nitrogen or moisture stress. All of these aphid species are a concern, however, because they can transmit barley yellow dwarf virus.
Barley yellow dwarf virus (BYDV) usually starts to become evident this time of year and is most easily seen in barley, but the characteristic yellow foliage can also be evident in wheat and oats. This disease can be confused with nutritional deficiencies, but with BYDV the more severe symptoms occur on the older leaves and symptoms begin at the tip of the newer leaves. The normal symptoms of the disease include stunted foliage growth, reduction in root growth, chlorosis, and striping from leaf tip towards the base. In wheat and oats, the plants may exhibit a reddening of older leaves. For pictures and more information on BYDV, see the Penn State fact sheet.
While BYDV is mostly passed to plants by aphids in autumn, spring transmission is possible. The disease itself cannot be treated, so it is necessary to focus on aphids with an integrated management plan, beginning in the fall by choosing to plant resistant varieties, which are available for barley. Resistant varieties can work well to complement the suite of natural enemies, which eat aphids and often control their early season populations (pesticide application can disrupt this natural control). Because aphid populations are very patchy, preventative insecticide applications are unlikely to be useful. Scouting is the key to finding aphid populations that exceed the economic threshold. The threshold published in the Penn State Agronomy Guide. This threshold was not based on the current higher price of wheat and other cereals, but growers should be wary of expecting a yield advantage for spring applications of insecticides against typical populations of these cereal aphids.