Posts Tagged ‘aphids on grain’

Aphids Prevention and Barley Yellow Dwarf Management

Thursday, August 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu, Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

As discussed in the article, Review of Barley Yellow Dwarf in 2012, the spread of barley yellow dwarf virus (BYDV) is completely dependent on aphids transmitting the virus which causes the infection. There are four aphid species occurring in Delaware that are capable of transmitting BYDV from infected grasses into wheat including the English grain aphid, bird cherry-oat aphid, corn leaf aphid, and the greenbug. For photos to help you identify aphids go to: http://kentagextension.blogspot.com/2007/10/know-your-small-grain-aphids.html

Aphids can infest small grain fields in the fall and again in the spring. The number of aphids arriving in fields in the fall is often dependent on the growing conditions the preceding summer. In general, cooler summer conditions with adequate rainfall followed by a warm, dry fall favors aphid development, especially in early planted fields. In drier summers, fewer aphids are produced due to reduced host plant quality. It should be noted that greenbug aphids (which cause direct damage to small grains as well as transmit BYDV) are favored by cool, late summer conditions. Aphid population densities in the fall are also affected by when the first hard frost occurs in relation to wheat seedling emergence. Crops that emerge long before a hard freeze have a greater potential for aphid infestation (and exposure to BYDV). Planting after the fly free date can help to help to manage aphids as long as the freeze occurs when expected. Aphids arriving in the fall will continue to feed and reproduce as long as temperatures remain above 48°F.

In areas where you have seen BYDV in the past, where you are planting early (before the Hessian fly-free date), or you have seen direct damage by greenbug aphids, a commercial applied seed treatment which includes an insecticide would be a good control option for fall infestations. Another option would be to scout fields and apply a foliar insecticide. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. The most important time for controlling aphids in the fall is the first 30 days following emergence. The second most important time is the second 30 days following emergence. So it will be important to scout wheat starting at plant emergence if you plan to use a foliar insecticide for fall aphid management. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

Since the incidence of BYDV has not been widespread in past years in Delaware and Maryland, we do not have current data from our area evaluating thresholds to time sprays for fall aphid management. The following thresholds from Kentucky (included in the above fact sheet) could be considered when making a decision to apply a fall foliar insecticide : (a) the first 30 days after planting treat if you find an average of three or more aphids per row-foot, (b) from 30-60 days after planting treat if you find six or more aphids per row-foot, and (c) more than 60 days after the plants emerge treat if you find ten or more aphids per row-foot. Depending on weather conditions, a second application could be needed, especially if temperatures remain warm. As we saw this past season, aphid populations remained high throughout the winter and early spring so you will need to continue scouting if conditions remain mild again. They also indicate that in some years these thresholds may be too high and in others too low but currently this is the best available information. In addition, the risk of BYD infection varies from year to year. At this point, we are still not certain if the 2012 season was just an unusual one for BYD or if we will continue to see an increase in problems. We hope to survey for aphids this fall and evaluate these thresholds under our conditions.

Scout Small Grains for Aphids, Winter Grain Mites and Cereal Leaf Beetle

Friday, March 28th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Recently we are receiving reports of high levels of aphids in barley and wheat fields. The fluctuating temperatures as well as continued dry conditions have been favorable for aphids. As indicated in a previous newsletter, cool, dry conditions generally favor spring outbreaks of aphids. This type of weather allows the aphids to survive and reproduce. Although natural enemies can keep aphids under control, cool dry weather in the spring often allows aphids to reproduce rapidly whereas their natural enemies reproduce slowly. Beneficial insects that attack aphids reproduce slowly at temperatures below 65°F, whereas aphids can rapidly increase when temperatures exceed 50°F. A number of insecticides are labeled for aphid control in wheat including: Baythroid, Baythroid XL, Dimethoate 4E, Lannate LV, Mustang MAX, Penncap-M, Proaxis, and Warrior. Materials labeled for aphid control in barley include Lannate, Penncap-M and Warrior. Check the labels for restrictions and harvest intervals. The recent Virginia Ag Pest Advisory from Ames Herbert indicates that they are hearing of many wheat (and some barley) fields with unusually high aphid numbers. Please use the following link for his comments on aphid management in wheat. (http://www.sripmc.org/Virginia/View.cfm?lngNewsID=487)

We continue to receive report of wheat fields with damage from winter grain mites. Remember, this mite is favored by cooler conditions. No thresholds are available for this mite pest. As indicated in the most recent Virginia Ag Pest Advisory written by Tom Kuhar, these mites have been found almost exclusively in no-till wheat situations. Very little is known about this sporadic pest; however, experience in Virginia this season indicates that that high densities of these mites can significantly affect plant vigor and growth. Although we have no experience with winter grain mite control in wheat, materials that have appeared to provide control in areas to our south include the pyrethroids (Warrior, Mustang MAX) and certain organophosphates (dimethoate). Note that dimethoate may not be effective when temperatures are below 60°F. Be sure to follow the rates and usage restrictions on the labels.

As temperatures increase in April, be sure to look for cereal leaf beetle adults, especially along field edges that border woods or in protected areas. Adult beetles feed along the veins of grain leaves leaving characteristic narrow linear holes parallel to the leaf veins. Although they do not cause much damage, you should routinely check these areas since this is where you are likely to find the first eggs and larvae. Larvae can feed heavily on leaves, especially flag leaves, and can quickly cause significant yield reductions if they exceed the economic threshold of 25 eggs/young larvae per 100 tillers.

Management of Aphids: Barley Yellow Dwarf Transmission and Direct Aphid Damage in the Spring

Wednesday, March 26th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu, Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu and Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

We are starting to receive questions regarding the need to spray for aphids in late winter and early spring in regards to both barley yellow dwarf virus (BYDV) transmission and direct aphid damage. Although fall conditions were favorable for aphids (warm and dry), we did not see an increase in populations in many wheat fields until late November and early December. In addition, there have been reports of a second period of population increase in late January and early February.

All of the aphids found in Delaware wheat fields are capable of transmitting BYDV. However, the virus strains that cause barley yellow dwarf are generally transmitted to the wheat in the fall or early spring before growth stage 4. For aphids to successfully transmit the virus in the most efficient manner, they normally need between 12 and 30 hours feeding to acquire the virus, and then 4 or more hours of feeding to transmit it. However, aphids are capable of acquiring the virus after feeding on infected plants for only 30 minutes. Once they acquire the virus and it is allowed to incubate for one to four days, they can transmit it to healthy plants for the rest of their life. (more…)