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.

Vol. 12, Issue 7, Published 4/7/2021

Over the last several years, there has been a tremendous amount of research activity towards the development of autonomous agriculture vehicles. A quick internet search will reveal over 50 companies or university research groups working in this space. A question I get often from groups developing such platforms is “What is a good agricultural application for our lightweight “robot”?”. It’s a great question, and for Arizona vegetable production, it’s also one that I’m not sure I have a satisfying answer for.

The calls I get regarding autonomous robots are mostly related to automated weeding applications. Automated weeding machines are commercially available, but their adoption has been limited not because of labor costs for tractor operation, rather it is the lack of the development of a functional and cost-effective means for identifying and removing weeds.

For decades, researchers have been attempting to develop sensing systems that are able to reliably detect weeds. Techniques such as 2-D and 3-D color imaging, x-rays, hyperspectral sensing and artificial intelligence have been tried (Slaughter, 2014; Bender et al., 2020). The best performing systems provide about 96% accuracy, meaning that 4% of the crops plants are identified as weeds and would be destroyed by the weeder. For high value vegetable crops like lettuce with gross revenues of roughly $10,000 per acre, killing 4% of the crop equates to $400 per acre of losses. Economically, this does not make sense as hand weeding labor costs are typically $300 per acre or less. The other main issue is that current automated weeding technologies are not highly precise and provide only partial control. Our studies with these types of machines have shown that these systems remove only about 1/3^rd of the in-row weeds (Lati, et al., 2016) and a follow up hand weeding operation is often necessary. To be highly cost effective, elimination of the hand weeding step is needed.

In short, my recommendation to research groups asking about applications for autonomous robots is that their time and technical skills would best be served developing reliable crop/weed differentiation systems and a technique to remove a very high percentage of weeds.

References
Bender, A., Whelan, B. & Sukkarieh, S. 2020. A high‐resolution, multimodal data set for agricultural robotics: A Ladybird's‐eye view of Brassica. J. Field Robotics. 37(1): 73-96.

Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.

Slaughter, D.C. The biological engineer: Sensing the difference between crops and weeds. Autonomous robotic weed control systems: A review. Computers and Electronics in Agriculture 61(2008): 63-78.

Malva (malva parviflora) is one of the oldest and most pervasive weeds that that we deal with here. It is also known as little mallow or cheeseweed and is in the same family as cotton, okra and hibiscus. It is often classified as a winter annual but survives all year in this region. It has a deep taproot and can grow in compacted clay or sand and in freezing conditions and high temperatures It provides a refuge for insects and diseases that can damage several crops.

Malva is easy to identify both as a seedling and mature plant. The seedlings are distinctively  heart shaped and the mature plant is broad and palm shaped. It is very vegetative and can grow to 6 ft.

The deep tap root of this weed makes it difficult to cut out after it is established. Its response to herbicides id somewhat unusual. It is very sensitive to contact herbicides that do not move into the plant. These include Goal, Sharpen Gramoxone , Rely,Aim and others. However, it is not sensitive to systemic herbicides like 2,4-D and Glyphosate. It reproduces from seed and can be controlled preemergence with many of the same preemergence herbicides used in cotton like Prowl or Treflan. The seed pods are wheel shaped which is where the name cheeseweed comes from. Each seed pod contains 10 to 12 seeds

Area wide Insect Trapping Network   VegIPM Update, Vol. 14, No. 19, Sep 14, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts beginning to increase, but a little below average for mid-September
 
Beet armyworm:         
Trap counts increased in most locations, bet well below average for mid- September.
 
Cabbage looper:         
Cabbage looper numbers remain low consistent with early September.
 
Diamondback moth:       
DBM moths starting to become active in some traps, about average for this time of the year.
 
Whitefly:                      
Adult movement increased in the past week, about below average for this time of year.
 
Thrips:                          
Thrips adults increased slightly in some locations (Tacna, Dome), and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during September. 
 
Leafminers:                  
Adult activity up in a few locations (Yuma Valley), below average for mid-September.