Featured Pest: Aphids
With the multiple challenges growers face – some of which include weed resistance, new disease races and damaging insects – it’s important to continue to remind them of available management options, as well as new technologies that can help improve their operations. In each issue of the Cereals Market Update, Syngenta will track and tackle your biggest “Pest Pet Peeve." In this issue, the featured pest is the aphid.
Tiny, soft-bodied insects known as aphids can often be found in wheat and barley fields throughout the growing season. Typically lingering on plant leaves or stems in cereal fields, aphids range in type and vary by region. Adult aphids can be up to a tenth of an inch long with pear-shaped bodies, and they may be winged or wingless.
Russian wheat aphids are a common, highly damaging species in wheat and barley and can survive on crops or grasses all year. Sporting rather short antennae, Russian wheat aphidsare small, lime-green pests with elongated, spindle-shaped bodies. The absence of prominent cornicles distinguishes this species from other aphids. Additionally, their projections are above the tail, which gives them a “double tail" appearance when viewed from the side. When they feed, Russian wheat aphids inject a toxin into the crop, causing discoloration in some wheat varieties, such as white or yellow longitudinal streaks on the leaves and stems. These aphids are typically more cold-tolerant than other grain aphids and can survive exposure to freezing temperatures.
As a result of their feeding, cereal crops may become stunted, display flattened tillers, develop poorly-formed grain heads, produce curled leaves, and, in cold weather, turn purple. High populations that are left untreated can cause severe yield loss. Depending on geography, early fall populations reaching 20 to 30 percent infestation may warrant an insecticide treatment, but risk of yield loss from Russian wheat aphid is highest when infestations develop in early spring.
Other aphid species cause damage by vectoring a crop-stunting viral disease called barley yellow dwarf virus (BYDV). Many researchers agree the following four species are the most common of the BYDV-transmitting pests:
Bird cherry-oat aphid: Dark green to almost black in color with a red-brown area on back of abdomen. Antennae are nearly as long as the body.
Corn leaf aphid: Blue-green with a fuzzy appearance. Body is flatter and longer than that of the bird cherry-oat aphid.
English grain aphid: Green to brown to pink with long black cornicles (tailpipes) that reach past the end of the body. Legs are long and black.
Greenbug: Pale green, smaller than the above-mentioned species, and with a very distinct dark green band down the middle of the back. Antennae are shorter than the body, and their relatively short cornicles have black tips.
Scouting for aphids in wheat and barley is a critical practice to prevent unwanted populations, potential crop injury and yield loss.If left uncontrolled, aphids can cause flag leaf and developing grain-head damage, in addition to lowering grain test weight, reducing the amount of developed kernels and stunting kernel size. And the crop impairment doesn’t stop there.
Caution: Barley Yellow Dwarf Virus
Aphids can acquire BYDV by feeding from one infected source and can subsequently transmit BYDV to another field. The virus thrives in cool, moist seasons due to continued plant growth and aphid activity. Symptoms of BYDV include: underdeveloped root systems, patches of stunted plants, winterkill, decreased tillering, discoloration of the crop, yellowing of flag leaf from tip back, delayed maturity and nutritional disorders – so be sure to detect these signs. Washington State University notes this disease can occasionally cause significant yield reductions in wheat.
In the Northern Plains, cereal crops may be at risk for BYDV and aphid infestations, as well. North Dakota State University Extension Entomologist Janet Knodel says many aphids carrying BYDV can come up from the southern regions and infect northern cereal crops. In such instances, insecticide treatment is a worthwhile option, especially since aphids are the sole transmitters of BYDV.
Research from the University of Illinois Extension regarding the effect of aphids on winter wheat yields suggests that the threshold is 12 to 15 aphids per tiller during seedling to boot stage. Neverthel