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

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

In 2018, we conducted a survey to assess current use and potential for adoption of automated technologies in vegetable crops. Many of you participated. The results are summarized in Tourte and Siemens (2018). One of the perhaps surprising results was that only 30% of growers currently use automated weeding machines. Although most growers had tried automated weeding machines, over 75% were either somewhat satisfied or not satisfied with the technology. The top concern and barrier to adoption was reliability. Commercialized automated weeders utilize metal blades that move in and out of the crop row to cultivate weeds between individual crop plants as the machine moves through the field. The high number of moving parts and complexity of operation limits their reliability.

As an alternative, we have been investigating the use of updated versions of older, simpler, “proven” technologies for weed control. These are camera-guided cultivators and mechanical in-row weeding tools. Camera-guided cultivator’s use a forward-looking camera to identify crop plant rows. Image processing techniques for differentiating between green, living plants and a brown, soil background are well known and robust. The cultivator’s tools are attached to a toolbar that is able to move relative to the tractor via actuation of a hydraulic cylinder or steerable coulter. Camera-guided cultivators have been commercially available from several manufacturers for decades.

The in-row weeding tool we have been experimenting with is termed a “finger weeder”. Finger weeders are fingered wheels made from flexible rubber. Pairs of the ground driven wheels are positioned over the crop row such that the fingers on adjacent pairs overlap slightly. In this configuration, small in-row weeds are uprooted while well rooted crop plants remain anchored to the soil and unharmed. These types of devices were first commercialized about 70 years ago and there are several European and domestic made models currently available in the U.S. 

We evaluated the use of a camera-guided cultivator and finger weeders with the aim of providing an improved and alternative method of controlling herbicide resistant weeds in cotton. Results of the 2-year study showed that finger weeders could be used in small cotton (1-2 leaf) without causing crop injury. Finger weeders were found to be effective at controlling small broadleaf weeds (less than ~1.5” in diameter). In experimental trials with heavy weed pressure, better than 50% of the in-row broadleaf weeds were controlled using the device. Larger broadleaf and well-rooted grassy weeds were not well controlled. This was expected as the devices are not designed for this purpose. Timing is critical for good performance.

Self-steering, camera-guided cultivators were found to be highly accurate and allowed cultivating tools to be positioned within 1.75” of the seed row (3.5” uncultivated band).  Utilizing the technology improved weed control by 60% as compared to conventional cultivation (Lillistons). This is an impressive, and logical result. The uncultivated band was reduced from 10” to 3.5”, or 65% and weed control efficacy was directly proportional to the decrease in the width of the uncultivated band.  Use of finger weeders in combination with the camera-guided cultivator was highly effective.  In 2019, plots had about 1/3rd as many weeds as compared to conventional (66% weed reduction) and in 2018, weed control was 85% for all weeds and about 93% for broadleaf weeds.

A link to an action video of the devices in action and trial results is provided below. It is not unreasonable to think that similar type results may be achievable in vegetable crops such as broccoli, cauliflower and cabbage that also have stems or stalks and are upright in nature. The devices have been tried and may have utility in most vegetable crops, including lettuce, and is an aim of future research. These technologies are readily available from dealers in Yuma, AZ and Salinas, CA.

Precision Cultivation Technologies for Improved Weed Control in Cotton Action Video Link –

https://youtu.be/iDnEH2-vsdc

References
Tourte, L. & Siemens, M.C. 2018. Assessing use of automated (mechanized) technologies in vegetable crops. Salinas Valley Agriculture - ANR Blogs.  4 pp. Davis, Calif.: University of California Davis. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=28921.

This is the time of year when people start to regret not controlling weeds earlier in wheat. Uncontrolled weeds begin to become more visible and both the crops and weeds are too big for most herbicides. The weeds not only produce millions of little time bombs (seeds) but can contaminate the crop, increase moisture and make harvest difficult. There are some herbicide options at this point, but none are great and all of them can only be applied when the wheat is at least in the hard dough stage and the crop is essentially done.

If the wheat is still developing both Simplicity and Osprey will control some big broadleaf and grass weeds. They may not be killed but they likely will stop growing. They can only be applied up to the jointing stage and most vegetables cannot be planted for 5 to 9 months following simplicity or 10 months following Osprey. The growth regulators (2,4-D, dicamba, MCPA and others) can only be applied up to tillering or the heads could be distorted and yield reduced. 

All of the preharvest herbicide options can only be applied when the wheat is in the hard dough stage and the crop is essentially finished. So, if the wheat is too far along now, you likely will have to wait. A few of the options include:

Glyphosate:
Do not use on wheat grown for seed. There is a zero tolerance for this herbicide in wheat for export to some countries and it also has the potential to reduce seed germ. This may be an option, however, for grain intended for other uses that is seriously contaminated with weeds. Applying glyphosate too early will damage the crop. There is a preharvest interval of 14 days and this treatment is likely to be slow. Application will have to be by air and drift should be avoided as glyphosate is none selective.

Aim/Shark
This is a contact herbicide and will work as a desiccant without systemic activity. There is a preharvest interval of 3 days and results can be slow. Systemic activity is not necessary since this will be used as a burndown harvest aid treatment. Paraquat is not registered for wheat.

Growth Regulators (2,4-D, Clarity, Dicamba)
Drift Hazard These are highly systemic and volatile. They will need to be applied by air and will be difficult to use after March. May be an option in isolated areas. There is a 7 to 14 day preharvest interval and the plant back interval can be from 1 to 6 months to many vegetable crops. It will not kill grasses such as volunteer sudan or Johnsongrass.

Sharpen
This is a contact, fast acting herbicide similar to Aim or Shark. It will not control grasses and has a preharvest interval of 3 days. Some markets will not accept grain treated with Sharpen so check first.

Ally
This is a systemic that will not work well if the weeds are stressed. It only controls broadleaf weeds.

Preharvest control of grasses such as sudan, summer and winter annuals. Most of the grass herbicides used in wheat (Discover, Tacoma, Simplicity and Osprey) are restricted to application before the boot stage of the wheat and have a plant back restriction of from 1 to 10 months. The use of the postemergence grass herbicides such as Clethodim and sethoxydim, will control most grasses but could reduce the viability of the wheat seed. 

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 23, Nov 17, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts continued to decline over the past 2 weeks across all locations and about average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in most locations, but well below average for late-October. Most activity in Yuma, dome and Gila Valleys.
 
Cabbage looper:          
Cabbage looper trap counts declined in most areas but increased in the Bard and Yuma Valley. Activity below average for early November.
 
Diamondback moth:     
Adults peaked in Gila and Yuma Valleys and above average in all locations for this time of year. Traps located adjacent to cauliflower and broccoli transplants had the highest trap captures 
 
Whitefly:                     
Adults remains active in Dome Valley, Wellton, and Roll consistent with melon crops completing harvest, but below average movement for this time of season. 
 
Thrips:                          
Thrips adult movement increased in most locations last week,  particularly in Dome Valley, Wellton, and Tacna. Activity about average for early November.
 
Aphids:                        
Aphid movement increased sharply in Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
 
Leafminers:                  
Adult activity increased sharply in the Gila Valley, Roll and Wellton; about average for this time of season.