Historically, our Areawide Pheromone and Sticky Trap monitoring for insects was terminated around the first of April as the produce season ended. Beginning 2 years ago however, we continued our Areawide Trapping Network throughout the summer to collect trapping data from all 16 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons. First, understanding the activity of some of our key pests when produce is not grown during the summer may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. Secondly, trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime/nighttime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, it gives me something to do in the summer.  So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to. We also continue to monitor thrips activity during the summer. This involves plant sampling using a dislodgement sampling method (beat pan) to determine the relative abundance of thrips adults and larvae on alfalfa, cotton, melons, wheat, Sudan grass, and weeds.  This is being conducted to supplement our yellow sticky trap data that only indicates thrips adult flight movement an area. With this plant sampling we should be able to determine the primary host plants thrips are colonizing in the cropping season during the long hot summer. We are also trying to determine whether these crops allow for the reproduction of thrips. So far, all the crops and weeds we have sampled have shown that thrips will reproduce and complete their life cycle on them. This is important, particularly for weeds, as we are trying to determine whether INSV can be survive the summer in the absence of lettuce. It is also important because it allows us to determine potential exposure of thrips to key insecticides like Radiant and Lannate for resistance management purposes. These crops essentially serve as untreated refugia that likely sustains insecticide susceptibility and is the reason these products are still effective against thrips.  We will be conducting this work throughout the summer, as well as through next produce season. We will periodically provide updates of these thrips monitoring results throughout the summer.  As my dad used to say, “to solve the problem, you must first understand the problem”.

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. 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, which contained two 25 ft rows of lettuce. Plants were thinned Jan 4, 2024  at the 3-4 leaf stage to a 12-inch spacing. 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.

Month	MaxTemp(°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Downy mildew (caused by Bremia lactucae) rating was done on variety Eblin, Bobcat, and 180 (partially funded by AILRC grant). Disease was first seen on 1-30-24. Please see attached excel file for chemicals application date. Disease rating was done on February 29^, 2024. Disease severity was determined  by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 0.5 = one to a few very small downy mildew colonies on bottom leaves; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most of the treatments exhibited activity against the disease to some extent. Latitude, Amara, Eject, Previcure flex exhibited good control in the variety Eblin (highly susceptible variety). Whereas Cevya, Stargus, Latitude, Amara, Revus, Thrive 4 M, Actigard, Instigo+Carbose+intereact showed activity against the pathogen in variety Bobcat. Please see excel file for the full list of chemicals and their efficacy. The lettuce variety 180 was resistant to the disease and no downy mildew was observed on the particular variety. No phytotoxicity was observed in this field.

Over the last 5 years, there has been a tremendous amount of investment, research and advancement in technologies for robotic/automated in-row weed control. This surge in recent activity is due in part to the advent of low-cost computing systems that utilize artificial intelligence and on-board imaging systems that identify and locate crop and weed plants in real-time. Entities developing these innovations are quite varied, ranging from small start-ups to well established companies to university and government researchers.  A quick internet search will reveal over 50 companies or university research groups working in this space. Many are domestically based, but the majority are from Europe where labor costs are very high and there is more resistance to and restrictions on herbicide use.

As you might expect, the diversity of approaches to the in-row weeding problem is wide. Methods for controlling in-row weeds include traditional methods such as mechanical hoeing and spot spraying, as well as alternative techniques such as spot spraying hot oil, flaming, lasers, high voltage electricity and microwaves. The use of fleets of small (1-row to 4-row) autonomous robots is a common theme, but there are also pulled implements equipped with actuators for automated weed removal.

I discussed some of these technologies at a technical breakout session at the 2020 Southwest Ag Summit. A link to the presentation is given below. It provides an overview of some of the latest developments, technologies and concepts for in-row weeding being worked on around the world. The presentation should be self-explanatory as it includes audio clips and company source information, but feel free to contact me for further information or if you have any questions. In future articles, I will discuss these technologies and concepts in more detail and how they might best fit into Arizona vegetable production systems.

Click on the video below to view the presentation on Technologies for
Robotic/Automated In-Row Weeding in Vegetable Crops:

Marestail and Fleabane have become increasingly widespread in recent years. This has occurred mostly in areas around field edges, roads, ditchbanks citrus groves and alfalfa fields. Marestail (Conyza candensis, also called horseweed), has been here for many years while Flaxleaf Fleabane (Conyza bonariensisis) is more recent. Both are in the Conyza genus and the sunflower family. Both are described as summer annuals, but they grow year round in the low desert. Although these two weeds are easy to distinguish once they are established and have several leaves, the seedlings look very similar. They form a rosette like shepardspurse, soon after emerging. After they bolt Marestail puts up a tall central stem that is dark green with long thin leaves. Fleabane, on the other hand, does not have a central stem but has several branches with smaller, grey thin leaves. Marestail can get 10 foot tall while fleabane rarely gets taller than 3 to 4 feet.(See picture below)

Controlling both of these weeds can be difficult because they grow rapidly, and plant populations have developed resistance to Glyphosate in many areas. Glyphosate still works well on Marestail in many areas here but there have been increasing misses. This is a characteristic of resistance, but it has not been tested or confirmed here. It has been confirmed throughout California. We did not have these weeds in many of our older herbicide trials and are now working to update our information on herbicides in alfalfa and citrus, specifically for these weeds and with some of the newer herbicides. In a few of our older trials where we had some marestail we did have good control with 2,4-DB but only partial control with trifluralin. These weeds can germinate any time of the year and trash on the surface will reduce control in citrus. We did not have fleabane in these early trials. We have had good control with Sharpen (Treevix, Kixor) postemergence and Chateau preemergence on many broadleaf weeds but do not have enough data on fleabane or marestail yet. It is on the labels for both herbicides and we will have current data later this season.

Results of pheromone and sticky trap catches can be viewed here.
Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 15, July 24, 2024

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts increased in Roll and Yuma Valley; about average to previous years.
 
Beet armyworm:          
BAW moth counts increase in Tacna and Wellton; comparable to previous summers.
 
Cabbage looper::          
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:      
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to increase consistent with disking of late melon fields and volunteers.
 
Thrips:                          
Thrips adult activity continues to decline, comparable to mid-summer.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity about average for early July.