Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

Damping off is a common problem in spinach. This season we have observed the occurrence of the disease from Imperial valley, to Yuma and all the way to Wellton.

Symptoms of damping‑off and root rot consist of poor seed germination, preemergence death of seedlings, postemergence death of newly emerged seedlings, stunted plants, yellowed lower leaves,  general poor growth, wilting, and eventual collapse and death of older plants. The upper taproot may be girdled by a necrotic lesion, or the tip of the taproot may be necrotic. In severe cases, nearly all roots may be girdled or rotted off. Damping-off is problematic in spinach production areas throughout the world. Severity is influenced by cultivar, soil texture, irrigation, and pathogen populations. Severe damping-off is associated with clay or poorly draining soils with a history of frequent spinach production. While all stages of spinach can be infected by root rot organisms, newly emerging plants and young seedlings are very susceptible.

Symptoms are more prominent in areas with poor drainage. These spinach problems are caused by a complex of pathogenic soil fungi that include one or more of the following: Fusarium oxysporum, Pythium (several species), and Rhizoctonia solani. These fungi are present in most soils and can get aggressive and cause loss when the environment is favorable. However, aboveground symptoms of plants that are overwatered are similar to symptoms of root rot. Excess water can damage roots, causing tan to brown, water‑soaked symptoms on roots even if no pathogen is present.

Management
Plant spinach in well draining soils. Prepare seed beds so that even, rapid germination is enhanced. Carefully manage the irrigation schedule to prevent flooding and saturated soil conditions. Plant seed that is treated with fungicides and fumigate the beds. Preplant application of mefenoxam will only control damping-off caused by Pythium. Avoid planting consecutive spinach crops and practice good crop rotation.

Always remember the disease triangle, the necessity of a susceptible host, the favorable environment, and virulent pathogen. To create unfavorable environment avoid overwatering, do light but frequent irrigation to avoid standing water in the field, schedule watering in the morning or earlier part of the day. Addition of soil amendments to increase microbial activity can be helpful.

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.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

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

Corn earworm: CEW moth counts increased in most traps; about average for early October.

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

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

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

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

Leaf miners: Adult activity light in all areas, about average for this time of season