Now that worm pressure has slow down a bit, you’re probably thinking about what’s next.   With the seasonal transition to cooler temperatures beginning to occur, along with shorter days and consistent N-NW winds, you will likely begin to see an increase in winged aphids showing up on desert produce crops. Winged aphid numbers on yellow sticky traps were noticeably higher in the Bard, North Gila and Yuma Valleys over the past week.  This is not a surprise; experience tells us that this is an annual occurrence.  The key aphid pests found on winter produce (i.e., green peach aphid, foxglove aphids, cabbage/turnip aphids) do not over-summer here, rather they migrate into our cropping system from mountainous regions of southern California via wind currents during the fall. They can also hitch a ride on transplants originating from the coast.  We’ve already seen a little of that this fall.  Once the aphids reach our desert valleys, they typically land on native vegetation and then into produce fields, moving among weeds and crops until they find a suitable host to feed and colonize on.  They might show up earlier this year given how dry the surrounding desert is.  No need to panic if you suddenly find a few winged aphids on a lettuce plant. But it is important that you correctly identify the aphid species present.  This time of the year it’s not uncommon to find winged aphids on lettuce that do not colonize the crop. For example, in the past couple of weeks PCAs have been reporting winged cowpea aphids on their lettuce and Cole crops. Not surprising given the high numbers infesting alfalfa this fall.  Once the weather really cools off, they should disappear. Other examples of winged aphids that can be found on produce crops would include aphids that colonize small grains (i.e., oat bird-cherry aphid) or alfalfa (i.e., blue alfalfa aphid).  Because these aphid species will not colonize produce crops, it is important to be able to distinguish them from the aphids that do colonize and require management to prevent problems at harvest (i.e., green peach aphid, foxglove aphid, lettuce aphid, cabbage aphid, turnip aphid).  Proper aphid ID can also influence your choice of insecticide, but more on that in a later update.  Don’t be surprised if you start finding small colonies of cowpea aphids or melon aphids showing up on frame leaves in lettuce. That is a common occurrence every fall.  Not to worry, experience has shown us that although small cowpea aphid colonies may be found on lettuce, the populations generally stay low on the plant on the frame leaves and rarely increase to levels causing contamination issues.   But you never know, so keep a close watch out for these early aphids in your crops. Bottom Line:  proper aphid identification is important; it can save a PCA time and money and prevent unnecessary insecticide applications. If you find an unusual aphid in your produce, don’t hesitate to drop it by the Ag Center and we’ll get it identified for you.    If you want to make fast and accurate IDs, you might use the attached publication Aphid Identification in Desert Produce Crops that can assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole crops.

Name that pest

In arid and semi-arid regions, water is our first limiting factor in a crop production system, followed closely by bio-available nitrogen (N).  Thus, our management of water and N are critically important to produce a healthy crop with good yields and quality.
 
Water and nutrient demands coincide with the fruiting cycle and efficient management of irrigation water and plant nutrients is enhanced by tracking crop development in the field.  The use of heat units (HUs) with 86/55 ^oF upper and lower thresholds can be applied to warm season crops in the desert Southwest in relation to the thermal environmental impacts on the development of all crop systems (Brown, 1989), including chiles, (Figures 1 and 2).
 
Crop Phenology Relationship to Water and Nitrogen Demand
 
Phenological guidelines have been developed for many crops, including New Mexico type chiles (Soto-Ortiz and Silvertooth, 2007 and Silvertooth, et al, 2010; Figure 1).  This phenological guideline can be used to identify or predict important stages of crop development that impact physiological requirements.  For example, a phenological guideline can help identify stages of growth in relation to crop water use (consumptive use) and nutrient uptake patterns (Figure 3).
 
This information allows growers to improve the timing of water and N inputs to improve production efficiency.  For some crops or production situations HU based phenological guidelines can be used to project critical dates such as harvest or crop termination.  Many other applications related to crop management (e.g., pest management) can be derived from a better understanding of crop growth and development patterns.

Figure 1.  Typical relationship between the rate of plant growth and development
and temperature.  Growth and development ceases when temperatures decline
below the lower temperature threshold (A) or increase above the upper
temperature threshold (C).  Growth and development increases rapidly when
temperatures fall between the lower and upper temperature thresholds (B).


Figure 2.  Basic phenological guideline for irrigated New Mexico-type chiles.

References
Brown, P. W.  1989.  Heat units.  Bull. 8915, Univ. of Arizona Cooperative Extension, College of Ag., Tucson, AZ.
Silvertooth, J.C., P.W. Brown, and S. Walker.  2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum).  University of Arizona Cooperative Extension Bulletin No. AZ 1529
Soto-Ortiz, R. and J.C. Silvertooth.  2007. A Crop Phenology Model for Irrigated New Mexico Chile (Capsicum annuum L.) The 2007 Vegetable Report. Jan 08:104-122. 

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.

At the UC Cooperative Extension 2024 Automated Technology Field Day in Salinas, CA a couple of weeks ago, 12 of the latest automated and robotic technologies were demonstrated in the field. Most were designed for weed control or thinning vegetable crops. Several of the technologies shown are relatively “new” for the 2024 season. These included laser weeders that also are capable of thinning lettuce (Fig. 1 & 2), a smart cultivator/side-dresser that cultivates between individual crop plants and simultaneously applies fertilizer at a variable rate depending on plant size (Fig. 3), a spot sprayer that utilizes superheated vegetable oil to kill weeds (Fig. 4), and a self-propelled machine that disinfests soil prior to planting using steam. Although the test runs were short, I was impressed with the possibilities for these machines. Company representatives said they will be in Arizona this upcoming season and are interested in meeting with growers. Company contact information can be found at their respective websites, or feel free to contact me if you would like additional information.

Fig. 1. Carbon Robotics’¹ (Seattle, WA) LaserWeeder^TM. The unit utilizes a vision
system to detect crop plants and weeds. A laser is used to kill unwanted plants.
The machine can be used for weeding or thinning lettuce crops (bottom).


Fig. 2. L&A¹ (Chico, WA) autonomous laser weeding/thinning robot. The unit is
equipped with a vision system to detect crop plants and weeds, and a laser to kill
unwanted plants. The machine can be used for crop thinning or weeding (weeded
carrot crop, bottom).


Fig. 3. Stout Industrial Technology’s¹ (Salinas, CA) smart cultivator/side
dresser. The unit is equipped with a vision system for detecting crop plants, and
blades that move in and out of the crop row to remove in-row weeds. Liquid
fertilizer (shown colored with blue dye) is applied at a variable rate depending on
plant size.


Fig. 4. Tensorfield Agriculture¹ (Union City, CA) precision spot spray weeding
machine. The unit has an 80” wide spray boom equipped with 232 individually
controllable spray nozzles to spot spray weeds with superheated vegetable oil
(bottom left, bottom right). A vision system is used to detect weeds and spot
spray resolution is ¼”.


Fig. 5. UA/UC Davis self-propelled band-steam applicator. Device injects steam
into the soil to kill weed seed and soilborne pathogens prior to planting.

[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

Question to IPM team:
I applied Raptor and Pursuit to an alfalfa field. Can you provide some information on the carryover and phytotoxicity to onions?
IPM Team:      We haven’t done plant back evaluations with these products. The soil persistence that is mentioned in the AZ PCA study guide is 2-4 months for the Raptor and 3-12 months for Pursuit. The label specifies longer replanting intervals for various crops and suggests that “before planting any crop not listed elsewhere in Rotational Crop Restrictions, a successful field bioassay must be completed. The field bioassay consists of a test strip of the intended rotational crop planted across the previously treated field and grown to maturity”.
An interesting journal article “Injury to Vegetable Crops from Herbicides Applied in Previous Years”, mentions In 1995, residual imazethapyr delayed tomato maturity but did not reduce tomato yield. Other vegetable crops were not injured by herbicide residues. Then in 1997 “imazethapyr carryover injured cabbage, onion, and tomato plants and reduced tomato yield most injury occurred at 2X and 4X rates¹.
The “Carrington Research Center in NDSU did an herbicide carryover study included here which presents the “response of onions to herbicides applied to soybean the previous year²” including Raptor and Pursuit.  Also, in this study (table below) onion injury was significant in the 2X and 4X rates.

Another “Evaluation of Pre and Post Emergence Herbicides on Yield Contributing and Quality Characters in Onion” found that “Imazethapyr @ 100 g a.i / ha as post emergence application (20 DAT) coupled with preemergence herbicides produced the lower (yield) values than weedy check as Imazethapyr found to be toxic to the Onion^3”.
The field study “Efficacy of imidazolinone herbicides applied to imidazolinone resistant maize and their carryover effect on rotational crops” showed sensitivity of rotational crops, from high to low, was the following: Beta vulgaris>Capsicum annum>Lycopersicum esculentum>Cucumis melo>Hordeum vulgare>Medicago sativa>Lolium multiflorum>Avena sativa>Pisum sativum>Allium cepa (onion)>Zea mays.
The label’s recommendation of doing a bioassay is very useful. Many factors can affect herbicide carryover and every case is different. Low soil moisture might not permit appropriate soil conditions for an efficient microbiological and chemical degradation of imidazolinone herbicides³. Other elements to consider are the soil texture, pH, soil temperature, microbial activity, photodegradation, previous crop, water applied after application of the herbicide, soil tillage intensity. The combinations of these elements could contribute to dissipation of these products. Also, having this information would help us determine the best IPM strategy.
 



References:

1. Greenland RG. Injury to vegetable crops from herbicides applied in previous years. Weed Technology. 2003;17(1):73-78. doi:10.1614/0890-037X(2003)017[0073:ITVCFH]2.0.CO;2
2. Herbicide Carryover Study, 1997 Richard Greenland
3. Evaluation of Pre and Post Emergence Herbicides on Yield Contributing and Quality Characters in Onion cv. N-53 M. Venkateswara Reddy* , K. Umajyothi, P. Syam Sundar Reddy and K. Sasikala
4. Efficacy of imidazolinone herbicides applied to imidazolinoneresistant maize and their carryover effect on rotational crops C. Alister1 , M. Kogan

Resistant varieties are crucial for effective insect pest management, more specifically in organic crop production. When growing crops organically, resistant varieties should be the first line of defense against insect pests. Compared to nonresistant varieties, insect-resistant crop varieties are less vulnerable to insect attacks or yield well despite insect attacks. 

Resistance in crops can be expressed through different mechanisms, including antibiosis, antixenosis, and tolerance. For the antibiosis mechanism, the resistant crops act on the life history traits of the pest, such as affecting fecundity, growth, development, and survival. Thus, this reduces the pest population. On the other hand, antixenosis is characterized by the ability of the crop to affect the behavior of the pest by deterring it after initial tasting or probing, which is non-preference. For the tolerance mechanism, however, the crops can sustain a high density of pests and still maintain their yield potential. In most cases, the overall resistance of a variety is a combination of all these three mechanisms. 

There is also a type of resistance called phenological resistance, field resistance, or pseudo-resistance, which is when the crop appears to be resistant because it is at a less susceptible stage when a pest attack occurs. This may happen either because of the rate of development of the crop or due to management practices implemented, causing the crop to escape the pest pressure. Thus, the implementation of proper agronomic practices plays a significant role in improving the ability of crops to resist pest attacks. 

In certain scenarios, additional insect control measures such as the use of bioinsecticides (in organic production) and natural enemies may be necessary in conjunction with an insect-resistant variety for comprehensive pest control. However, even in cases where additional control measures are required, the cultivation of a resistant variety can significantly delay and reduce the amount of insecticide applications needed. This underscores the economic, ecological, and environmental benefits of using insect-resistant crop varieties. 

Previous studies conducted at Yuma Agricultural Center demonstrated that resistant lettuce varieties can provide suitable control of aphids affecting lettuce in the region. Therefore, it is very important to consider cultivating insect-resistant lettuce varieties for suitable management of aphids in organic lettuce production since biological insecticide options are currently limited. My lab is planning to evaluate several lettuce varieties to determine lettuce varieties that carry resistance against aphids in an attempt to generate applicable information on varieties that could fit well within the production practices and environmental conditions of Arizona’s vegetable-growing regions. 

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased considerably y in the past 2 weeks and about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa
 
Cabbage looper:         
Cabbage looper numbers remain low consistent previous years.
 
Diamondback moth:      
DBM moths were not caught in any trap since June; average for this time of the year.
 
Whitefly:                      
Adult movement decreased in past 2 weeks consistent with previous years
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and slightly above average for early August