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Areawide Insect Trapping Network

Vegetable IPM Updates Archive

Insect Management

Oct 17, 2018

Be Aware of Corn Earworm in Head Lettuce

With head lettuce crops beginning to rosette and folding-in to form heads, it would be wise to keep a keen eye out for corn earworm (CEW). This year could be particularly important as pheromone trap catches this fall have been much higher than we’ve seen in recent years (see graph below and Areawide Trap Network). Although pheromone trap counts don’t always correlate to field infestations, the last time we saw significant fall larval populations in the field was in 2014. What’s scary is that moth counts this week are higher than what we saw in the fall of 2014. Furthermore, PCA’s have recently reported the presence of CEW larvae on lettuce in Dome Valley and Wellton. At the Yuma Ag Center we can find larvae on ~3% of pre-heading stage plants (that’s above threshold). CEW can be very damaging in early fall head lettuce crops where once head formation begins larvae will usually bore into the head almost immediately upon hatching. Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera larvae, rendering the heads unmarketable. Larvae may enter the head from any point on the plants, but can often be found burrowing in from the top half of the head. If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is virtually impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head or cup over, you should treat as soon as possible. Moreover, during late October and early November it is probably a good idea to prophylactically apply a pyrethroid, methomyl or acephate when heads begin to form. The UA nominal threshold for CEW in head lettuce from the beginning of heading to harvest is 1-2 larvae / 100 plants (1-2%). Repeated insecticide treatments may be required to maintain low population levels if heavy pressure is sustained near harvest. Most contact insecticides recommended for Lep larvae are active against CEW. Lab bioassays have shown that CEW larval mortality is most rapid when exposed to Lannate, 0.5 lb (>90% mortality in 1 hr after exposure) and pyrethroids, high rates (>90% mortality in 3 hrs), followed by Radiant, 5 oz (>90% mortality in 6 hrs). By 24 hrs, mortality was 100% for all the treatments. For more information on CEW management and control recommendations see Corn Earworm Management on Desert Produce and the 2018 Lep Control Chart.

To contact John Palumbo go to: jpalumbo@ag.Arizona.edu

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Soil Science

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Plant Pathology

Jul 10, 2024

Virus transmission: Part III (2024)
Viruses vectored by insects

We are on the final section of virus transmission. Virus transmission by insects is one of the most efficient and economically important transmission in agriculture. When you have insects in your crops, not only you are losing your crops because of feeding/chewing by insects, a lot of insects also act as a vector of plant viruses.

Seven out of 29 orders of insect feeding on living green land plants are vectors of plant viruses.
Insect transmit viruses in 4 distinct modes:
1. Non persistent transmission: The insects can acquire the virus in a matter if seconds/minutes and they are immediately viruliferous. The virus in retained in the stylet of the insect and are transmitted to the next plant the insect feeds on. The virus is retained in the vector only for few minutes and is lost after insect molting. Most viruses transmitted by aphids are non persistent. So when you see few aphids in your melon field and see cucumber mosaic virus symptoms 1-2 weeks later in your field, don’t be surprised. Aphids are efficient vectors, and since viruses are systemic it takes anywhere from few days to 2-3 weeks for the plants to show symptoms. Thus it is very important to manage insects in the field even if you don’t think the ‘pressure’ is not as high.
Viruses transmitted in non-persistent manner:
Papaya ringspot virus
Zucchini yellow mosaic virus
Watermelon mosaic virus
1. Semi-persistent transmission: The insects can acquire the virus in minutes/hours and there is no latent (incubation) period in the insect. The virus can stay in the insects foregut for hours and is lost after insect molting. Some species of aphids and whiteflies fall in this category. Example: Cucurbit yellow stunting disorder virus in melons transmitted by whiteflies.
1. Persistent circulative: Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus for weeks. Virus can be present in the vectors hemolymph but there is no multiplication of virus in the insect body. Vectors in this transmission includes: Aphids, leafhopper, whiteflies, treehopper.
Example: Beet curly top virus transmission by beet leafhopper
1. Persistent propagative: Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus throughout its lifespan. The virus can multiply in the vector system and often times the virus particles are also passed on to the insect offspring. Tomato spotted wilt virus is transmitted on persistent propagative manner by 9 different species on thrips.
Save the Date : 2024 Plant Pathology Workshop
When: August 29^th 8AM-12 PM ( breakfast and Lunch provided by Gowan Company and BASF)
Where: Yuma Ag Center, 6425 W 8^th Street
What will covered: Plant Pathology program Updates, past season field trial results (we
have some exciting results to share), Q&A to help better Plant pathology program,
Industry panel discussion for all your industry related questions! See you in few weeks!
To contact Bindu Poudel go to: bpoudel@email.arizona.edu

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Mechanization

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Weed Sciences

Aug 17, 2016

Weeds to Be on the Lookout For 2016

Despite the development of new herbicides and other control techniques, weeds are as much of a problem today as they have ever been. Those that can be controlled diminish over time while those that are difficult to control become more widespread. New weed species are constantly being introduced. Some of these become established and others never do for a variety of reasons including cropping patterns, climatic conditions, registered herbicides , management practices and other conditions. There are a few species that have become established in other regions around Yuma but have never become widespread here. Some that you should be on the lookout for are:

Common Groundsel (Senecio vulgaris)
This is a winter annual that is has been established in the surrounding states for many years. It first started to appear in La Paz County,Az. about 15 years ago and is now widespread there and in the Imperial valley. It is mostly in alfalfa but also present in many other crops. It is in the composite or sunflower family but is more difficult to control than most other weeds in this family. Oxyfluorfen will control small groundsel in cole crops but it is difficult to control selectively pre or postemergence in lettuce. It is best if you can germinate and kill it prior to planting.

This is classified as a summer annual but it can be found year round in the low desert. It is often confused with horseweed or marestail (Conyza canadensis). It has appeared in La Paz county in the Parker Valley, but has not known to be established in Yuma County. This weed is more gray green and hairy than the horseweed that has been in Yuma for many years. Fleabane characteristically branches from the base more than horseweed. Both can be difficult to control. Glyphosate resistant fleabane is becoming more widespread across the country. The horseweed that has been in Yuma for a long time still appears to be controllable with glyphosate.

This is similar to the littleseed canarygrass (Phalaris minor), that has been here for many years. The seedlings are different and it can be misidentified when it first emerges. The leaves are broader than littleseed and do not bleed when broken at the stem. Hood canarygrass was first identified last year in the south Gila Valley. We had not recognized it previously in Yuma County. The seed head looks similar but is different. The spikelets have a characteristic hook on them compared to littleseed which is smooth. Hood Canarygrass is difficult to control postemergence with clethodim (Select) or sethoxydim (Poast). Neither of these was effective last season.

To contact Marco Pena go to: marcop@ag.arizona.edu

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Specialty Crops

Areawide Insect Trapping Network

Aug 7, 2024

Area wide Insect Trapping Network (August 7, 2024)

Areawide Insect Trapping Network   VegIPM Update, Vol. 15, No. 16, Aug 7, 2024

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm:
CEW moth counts decreased areawide; about average to previous years.

Beet armyworm:
BAW moth counts decreased; comparable to previous summers.

Cabbage looper:
Cabbage looper numbers are low consistent with previous years and higher temperatures.

Diamondback moth:
DBM moths were not caught in any trap; average for this time of the year.

Whitefly:
Adult movement continues to decrease, average for this time of the year.

Thrips:
Thrips adult activity continues to decline, average for early August.

Aphids:
Aphid movement is absent and consistent with what we typically see during the summer.

Leafminers:
Adult activity declining and below average for early August.

To contact John Palumbo go to: jpalumbo@ag.arizona.edu

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