Increased Insecticide Use Protects Onions from Viral Infections

weeds

Onions infected with iris yellow spot virus

Iris Yellow Spot Virus (IYSV) was first discovered in the U.S.in 1989 infecting onions in the Treasure Valley of Idaho and Oregon. IYSV typically does not kill plants; however the virus reduces plant vigor and bulb size. Once plants are infected with IYSV, there is no cure. The virus is transmitted to onions by the feeding of an insect: onion thrips. The disease spreads rapidly in fields with large numbers of thrips. Losses up to 100% have been reported. Onion thrips populations are reduced by the application of insecticides in onion fields thus preventing transmission of the disease to onion plants.

Iris yellow spot virus pressure in this region has not been nearly as bad as it was last year, when it wiped out some onion fields. “The virus seems to have been held off well this year,” said Paul Skeen, who farms near Nyssa, Ore. Farmers in the Treasure Valley area of southwestern Idaho and eastern Oregon produce about 25 percent of the nation’s bulb onions and the virus is one of their main production challenges. It weakens the plant and reduces onion production. It can substantially reduce onion bulb size, which is important because larger onions fetch a higher price. The disease is spread to onions by thrips, and Skeen said many growers in the area started spraying for thrips earlier this season and they sprayed more often. Skeen started spraying 10 days earlier and sprayed every seven to 10 days as opposed to every 14-20 as he has done in past seasons. “I’ve got a good crop coming because I stayed on top of it. I think everybody’s been doing that,” he said.

While onion growers in the Treasure Valley area typically start their thrip spraying programs around Memorial Day, many started in early May this year, said Stuart Reitz, an OSU cropping systems extension agent in Malheur County. While onion growers in this area normally make about six applications for thrips in a season, many have made eight or nine already this year and a few are up to 10, he said. “That helped keep the thrips population down,” Reitz said.

Author: Ellis, S.
Affiliation: Reporter.
Title: Onion virus pressure not as severe as last year.
Source: Capital Press. August 8, 2014.

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Nematicide Applications Could Increase Food Production in Africa

Roots

Nematodes are invertebrate roundworms that are second only to insects in the number of species in the animal kingdom. One cubic foot of soil may contain millions of individual nematodes. Nematodes feed on plant roots. Damage and low yields caused by nematodes frequently go unrecognized or are attributed to other causes. Research in Africa has demonstrated that controlling plant-parasitic nematodes can increase crop yields dramatically.

“Sweet pepper, the second most important vegetable crop in Niger, after onions is grown all over the country, but the region of Diffa alone accounts for over 85% of national production. The area planted in 2008 exceeds 7000 ha with a production estimated at 120000 t.

The production is mainly exported to Nigeria and procures substantial income to the people of the region of Diffa.

The average fruit yield of the crop is about 17 t/ha. This is very low compared to the potential of the crop. This low yield is partly due to diseases and pests pressure, namely the damage caused by plant-parasitic nematodes. …Yield losses caused by these nematodes can reach up to 60% in heavily infested sandy soils.

The study assessed the effectiveness of Savanem 20 EC (Ethoprophos, 200g/l), a newly introduced nematicide on the plant-parasitic nematodes associated with sweet pepper.

Savanem increased the average yield by 37.1% and Furadan by 20.6%.

Savanem 20 EC, at the dose of 50 L/ha is effective against the community of parasitic nematodes on sweet pepper.”

Authors: Adamou, H., et al.
Affiliation: Institut National de la Recherche Agronomique du Niger (INRAN)
Title: On-farm testing of savanem 20 EC (ethoprophos) for control of plant parasitic nematodes associated with pepper (Capsicum annuum) in tillaberi (Niger).
Source: Asian Journal of Agricultural Sciences. 2013. 5[4]:83-87.

Canadian Onions for Long-Term Storage Depend on Fungicide Sprays

Late Blight Caused By Botrytis

Late Blight Caused By Botrytis

In eastern Canada, Botrytis Leaf Blight (BLB) of onions caused by the fungus Botrytis squamosa is the key disease for scheduling fungicide applications. BLB is characterized by silver halos on green leaves, followed by leaf tip dieback and leaf blighting, which reduces photosynthesis and consequently bulb size. Although there are some onion cultivars that are tolerant to the disease, they are not widely-planted in Canada because they are not suitable for long-term storage.

“There are no commercially available onion cultivars that are resistant to B. squamosa. However, a few of the early cultivars are known to be tolerant. These cultivars can produce a marketable yield under wet weather conditions and are grown on both conventional farms and organic certified farms for which there are no registered fungicides that are effective against BLB. However, these cultivars are not suitable for long-term storage; hence, they represent only a small part of the total onion acreage in northern climates. Consequently, in most onion production areas where BLB is a problem, the disease is managed through repeated applications of fungicides on a regular calendar-based schedule or following a leaf blight predictive system. Typical fungicide spray programs involve applying fungicides every seven to ten days from the four-leaf growth stage until sprout inhibitor application or 50% soft neck stage.”

Author: Herve Van der Heyden, et al
Affiliation: Compagnie de recherché Phytodata Inc. Quebec, Canada
Title: Comparison of monitoring based indicators for initiating fungicide spray programs to control Botrytis leaf blight of onion
Source: Crop Protection. March 2012. 33:21-28.

Onion Plants Die Without Insecticide Treatments

Onion Maggot Damage

Onion Maggot Damage

100,000-300,000 onion maggots overwinter on every acre of onions in northern states. The average number of eggs laid by a single female in the spring is about 50. The emerging maggots seek out the roots and bulbs of onions and tunnel into the bulb. Maggots feed for two to three weeks. Damaged plants are usually so severely injured that they wilt, dry out and soon disappear.

“Management of onion maggot Delia antiqua is an integral component of onion production in the northern United States and Canada. There are three generations of D. antiqua per year in the northern United States and infestations of first-generation D. antiqua typically cause the most serious damage because maggot feeding kills seedlings. If onion seedlings are not protected with an insecticide applied during planting, D. antiqua can reduce plant stands by one-half to near 100%.”

Authors: B. Nault, J.Z. Zhao, R. Straub, J. Nyrop and M.L. Hessney.
Affiliation:  Department of Entomology, NYSAES, Cornell University.
Title: Onion Maggot (Diptera: Anthomyiidae) Resistance to Chlorpyrifos in New York Onion Fields.
Publication: Journal of Economic Entomology. 2006. 99(4):1375-1380.