Consistent with the warm weather we have been experiencing lately, Lettuce aphids, Nasonovia ribisnigri, (aka., Red aphid) are beginning to show up in desert lettuce again. In the past week, we've positively identified lettuce aphid appearing on both head lettuce and romaine in Dome Valley and Wellton. In addition, we have picked up a couple of alate (winged) lettuce aphids on the Ag Center, but no colonization of apterous (wingless) aphids has been observed yet. However, previous experience has taught us that daytime high temperatures in the high 70's and low 80's are ideal for population growth. Thus, we anticipate that lettuce aphids will begin colonizing rapidly throughout March. A few things to remember about lettuce aphids relative to the other aphids we commonly see. First, the immature nymphs are small and have a red appearance, whereas the apterous adults are typically a large brown colored aphid with dark bands running across the abdomen. Second, among the crops we grow locally, lettuce aphids are only found on the lettuce types (Lactuca spp.). Lettuce aphids prefer to colonize the terminal growth, and can often be found in heads or hearts, whereas green peach aphids are often found on the frame leaves in high numbers before moving into the heads. Sampling should be focused in the terminal growth of young plants, and in the heads and hearts of older plants. Third, they can reproduce prolifically, producing many more winged alates than other species, which can quickly lead to widespread abundance throughout a field or a growing area. Finally, as the saying goes "he who hesitates is lost". If lettuce aphids are found on your lettuce, it is recommended that you respond quickly with an insecticide treatment. The product of choice is Movento at 5 oz/ac. Because of its systemic activity, Movento will reach aphids in the protected terminal growth. Be sure to include a penetrating adjuvant for best results at a rate of at least 0.25% v/v. It normally requires 7-10 days of activity before significant reduction in the infestation is observed. For more information please refer to the bulletin: "Lettuce Aphid on Late Season Produce"

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! 

Plans are firming up for the 2nd Automated Weeding Technologies Field Demo Day. We have penciled in an event date of Thursday, October 21st. The focus this year will be on the latest automated weeding technologies that are “new” since our 2018 event. I’ve been reaching out to multiple companies but am sure I’m not aware of all the cutting-edge technologies out there. We would love to showcase as many innovations as possible, so please contact me if you are interested in demoing your equipment or know someone that is. It’s an open invitation - private companies, and university and government researchers are all welcome!

Two closely related but different species of several summer annual grasses are common in the low deserts. In general, these are all easy to distinguish from each other in the field and they respond similarly to herbicides. Some of these and their distinguishing characteristics are:

Watergrass (Echinochloa colonum) and Barnyardgrass (Echinochloa crusgalli)
These are very similar but watergrass has purple bands or chevrons on the leaves and barnyardgrass often has awns or bristles at the end of the spikelets. Both respond the same to herbicides.

Red Sprangletop (Leptochloa filiformis) and Mexican Sprangletop (Leptochloa uninervia)
Red sprangletop is, in general, a lighter green color and has a finer seed head than does Mexican sprangletop which is darker green or gray and has a visibly coarser seedhead. Both form clumps or crowns that often survive through the winter months. Both are fairly tolerant to Poast (sethoxydim) and Fusilade (fluaziflop) but are controlled with high rates of Select (clethodim).

Field Sandbur (Cenchrus pauciflorus) and Southern Sandbur (Cenchrus echinatus)
Both of these equally miserable weeds are only found in sandy soils and fairly easy to distinguish. Field sandbur has thinner, gray colored leaves and yellowish burs that are longer than broad. Southern sandbur has darker and broader leaves and fatter red colored burs. Southern sandbur has a more compact seed head with distinctly more burs than does southern sandbur. Both of these are fairly tolerant to Poast (sethoxydim), Select (clethodim) and Fusilade (fluaziflop).

Southwestern Cupgrass (Eriochloa gracilis) and Prairie Cupgrass (Eriochloa contracta)
These similar grasses are fairly easy to distinguish in the field. Southwestern Cupgrass is one of the wider leafed grasses in the deserts. Prairie Cupgrass leaves are not as wide and are hairy. Southwestern is more branched than prairie and the ligule is shorter and less prominent. The branches are longer and fewer on prairie than on southwestern Cupgrass. Both respond the same to most herbicides.

Green Foxtail (Setaria viridis) and Yellow Foxtail (Setaria glauca)
Both green and yellow foxtail typically form clumps, produce lots of seed and stand more upright than many other summer annual grasses. They are not difficult to distinguish in the field. Green has a darker greenish or brown seedhead compared to the yellow. The leaves of yellow are generally longer and have more bristles (5-20) per spikelet than green, which typically has 3 or less darker colored bristles. Both respond the same to most herbicides. This link will connect you with a powerpoint presentation that will help in the identification of summer annual grasses in the deserts.

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

Corn earworm: CEW moth counts down in most traps over the last week; about average for early October.

Beet armyworm: Trap counts increased in several areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts increased in most locations, but still below average for this time of the season.

Diamondback moth: Adult activity spiked 2 weeks ago, particularly in the Yuma and Dome Valleys, but down over the past week. Average for this time of season.

Whitefly: Adult movement increasing Tacna consistent with melon harvests; overall about average for early October.

Thrips: Thrips adult movement peaked 2 weeks ago but down ovr the past week, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; below average for October.

Leafminers: Adult activity increased significantly last week in several locations, above average for this time of season.