Desert growers have begun planting fall melons and transplanting cole crops, while direct seeding of produce crops is just a couple of week away. Accordingly, PCAs and growers will soon be faced with a number of important insect management issues. As crops begin to emerge, they can expect to encounter a number of insect pests that have the potential to cause serious economic losses to crop stands. These include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillars (‘woolly worms’). These insects all have chewing mouthparts and most are capable of consuming large amounts of leaf tissue in a short period of time. Seedling crops at the cotyledon stage are most susceptible; these pests can devour entire cotyledons or outright kill small seedlings. If left unprotected, larger seedling plants (1-2 leaf stage) can sustain significant feeding damage on the terminal growing points or newly emerged leaves. Not only can this feeding stunt plant growth, but can result in lack of stand uniformity and ultimately, maturity at harvest. Host crop sources of flea beetle, cricket and "woolly worm" infestations include numerous summer crops (e.g., sudan grass, cotton and alfalfa) and weeds (e.g., purslane). We are currently noticing high numbers of flea beetles and crickets at the Yuma Ag Center on sudan grass and weeds. Salt caterpillars have not been detected, but are known to disperse from alfalfa and pima cotton. Experience indicates that melon fields planted adjacent to these crops/weedy areas are at a high risk from these seedling pests, particularly flea beetles. As summer crops are harvested or terminated during the next several weeks, these seedling pests typically move to the next available host crop; lettuce, cole crops and melons. Fortunately, there are many registered insecticide alternatives available that can be applied via sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., methomyl, neonicotinoids) that can cost-effectively minimize their abundance and damage to emerging produce and melon crops. Additionally, seed treatments are available for lettuce and cole crops that will protect stands from flea beetles. For more information on insect pests of leafy vegetables and melons at stand establishment please see Insect Management on Desert Produce and Melons: Pests at Stand Establishment.

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! 

For those of you interested in the latest developments in Vegetable IPM and/or in need of CEU’s, Yuma County Cooperative Extension has created online workshops that offer CEU and CCA credits for both AZ and CA. Current offerings are the recorded workshops from 2021 Southwest Ag Summit. There’s an ag mechanization session entitled “Advances in Weed Control Technologies”, and several others that readers of this newsletter may be particularly interested in including: “Integrated Pest Management Regulatory Update” “Pesticide-Related Updates: The Latest Presented by the Greatest” “Influence of Irrigation on Insect, Weed, and Disease Management” “Advances in Weed Control Technologies” “Integrated Pest Management in Vegetables”. Please recognize Yuma County Cooperative Extension Agricultural Agent Robert Masson who spearheaded this effort. Click on the image, or here to access Veg IPM workshops online.

Weeds that are outside of fields can still be harmful to crop production. This does not include ditch banks or fallow fields. Non-crop weed control includes weeds around buildings, roadways, equipment yards, fence lines etc. It is different than fallow ground or ditch banks weed control and includes places where crops are not grown. Weeds in non-crop areas can be a source of weed seeds that blow or are carried into places where crops are grown. They can also be a refuge for insects,  diseases and rodents. The reason that these herbicides are registered for non-crop areas is that they are broad spectrum and persistent. Some are registered for use in fields but at much lower rates than for non-crop areas. For instance, Diuron can be used on alfalfa at 1 to 1.5 qts/ac. but is used for non-crop areas at 12 qts/ac.

Herbicide	Weeds Controlled	Activity	Soil Residual	Comments
Bromacil	Broadleaves and grasses	Preemergence	1 to 2 years	The nuclear option Should be incorporated with water. Keep away from roots of desirable vegetation.
Hexazinone	Broadleaves and grasses	Preemergence and Postemergence	1 to 2 years	Keep away from roots of desirable vegetation. Incorporate with water.
Diuron	Broadleaves and grasses	Preemergence and Postemergence	2 years	Incorporate with water but do not leach into roots of desirable vegetation
Prometon	Broadleaves and grasses	Preemergence and Postemergence	1 to 2 years	Must be incorporated with water
Tebuthiuron	Broadleaves and grass. Good on hardwood trees	Preemergence and postemergence	2 years	Incorporate with water. Contact with even on feeder root of desirable vegetation can be lethal
Imazapyr	Broadleaves and grasses	Preemergence and post emergence	1 year	Primarily a postemergence herbicide but is readily absorbed by rootsif incorporated with water
sulfometuron	Broadleaves and grasses	Preemergence and post emergence	1 year	Must incorporate with water
Aminopyralid	Broadleaves	Preemergence	1 year	broadleaves only. Shorter soil residual for weeds but crops can not be planted for 1-2 years

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 17, Aug 21, 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 are up in south Yuma valley and Dome valley; about average for August

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 August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity declining and average for August.