With the fall produce season quickly approaching, now is a good time to begin thinking about Bagrada bugs. It has been four years since this invasive species first showed up in the desert, but it has clearly found a home on local cole crops. The graph below shows Bagrada bug abundance on untreated broccoli and cabbage plantings at the Yuma Ag Center over the past three years. Last year populations were higher during the fall than we’ve seen to date. Over the course of the summer, there have been reports of adults found in alfalfa seed, sudangrass and weeds, and Bagrada were found in the Yuma Valley as recently as this week on broccoli seedlings. So, what should a PCA expect for this season? Don’t know for sure, but do not become complacent just because you’re not finding any Bagrada on your first sets. It would be wise to assume they will eventually show up in some intensity in some of your acreage, and you should prepare for them accordingly. Monitoring for Bagrada at stand establishment should focus on fresh feeding signs on new plant tissue, and adults later in the day when they are most active. Research and anecdotal observations in fields conducted over the past 2 years suggests that direct-seeded and transplanted crops are most susceptible to Bagrada bug infestations during stand establishment (cotyledon to 4-leaf stage). Furthermore, results suggest that it doesn’t take a large number of Bagrada adults to cause significant stand losses, and/or crop injury. If you readily find fresh feeding signs and /or adults in young stands control should be initiated. This can include chemigation with pyrethroids, and using contact insecticides (pyrethroids, Lannate, Lorsban) once stands are lined out and pipe is pulled. After stands are established and plant size increases up to the 1-2 leaf stage, or on tagged transplants, consider alternating to dinotefuron (Venom/Scorpion) for protecting plants from Bagrada feeding. This neonicotinoid will also provide knockdown of adult whiteflies and nymphs. More information on Bagrada bug management on fall cole crops can be found in these Veg Update briefs: Bagrada Bug Management Tips for the Low Desert and Knockdown and Residual Control of Bagrada Bug with Foliar Insecticides in Broccoli: 2013 Efficacy Report.

Whenever we go to the field to evaluate a crop, there are typically three fundamental points we need to take into consideration that include: 1) stage of growth, 2) general crop vigor and condition, and 3) anticipate the next stage of development and what we need to do in managerial response.  These considerations are commonly focused on aboveground crop evaluations.  However, the root system, completely belowground, is an extremely important part of the crop condition to evaluate.
 
Root systems are responsible for all water and nutrient uptake by the plant and provides the physical anchoring and support of the plant structure.  Each plant and crop species has its own “personality” and growth habits and the nature of the root systems also vary among plants species.  Many plant species can have root systems that constitute ~ 50% of the total plant dry matter and we generally consider plants to have at least 30% of total plant dry matter allocated to the root systems.
 
Young plants will often develop some basic aboveground tissue to perform sufficient photosynthesis for establishment and then devote a high amount of the energy, carbohydrates produced, along with the nutrients and water from the soil to root system growth and development. Sometimes it can appear that plants are not growing rapidly while investing energy and resources into root system development.  The depth of the roots will vary according to the soil physical conditions and effective soil depth, soil fertility and salinity management, plant-available water, and of course the natural rooting characteristics of the plant.  
 
The effective root zone depth is the depth of soil used by the bulk of the plant root system to explore a soil volume and obtain plant-available moisture and plant nutrients.  Effective root depth is not the same as the maximum root zone depth. As a rule of thumb, we commonly consider about 70% of the moisture that is taken up by the root is obtained in the top half of the root zone; about 20% from the third quarter; and about 10% from the soil in the deepest quarter of the root zone.  The small and very fine root hairs are the most physiologically active portion of a developing root system.  It is important that the plants continue to develop and generate fresh young roots and an abundance of fine root hairs to maintain water and nutrient uptake.
 
Therefore, in scouting fields and making crop evaluations, examining the root systems is an important part of the process.  Leafy green vegetable crops need to develop a marketable plant in a relatively short amount of time and a strong root system is essential.  It does take more time and effort to check root systems and it is a plant destructive process since we need to literally excavate the roots.  So, it is also important be careful of where and how we sample plants and the root systems in a field.

We have learned a lot about viruses in the past few newsletter articles and one of the striking features of most plant viruses is that they always need a host. And the relationship between a virus and its host plant is very specific. So where do the viruses go when we do not have lettuce or melon in the field? And how do they come back at the right time to infect the crops?  (clue insect vector). The answer is weeds. A lot of the most economically important viruses are economically important viruses not just because of the losses they cause, but also because of the losses they cause in variety of plants. Viruses have small genome size that allows them to evolve faster. Viruses over time have evolved to adapt and increase their host range.
Below are some common viruses in agriculture and the number of plants they infect/overwinter. Keep in mind that there are many plants that can act as a reservoir for virus but have not been reported yet, so this is not an exclusive list. 
 
Alfalfa mosaic virus (AMV): Alfalfa, lettuce,indive, sunflower, datura, amaranth, different species of pigweed, milkweed, annual fleabane, ixeye daisy, hairy galinsoga, smallflower galinsoga, different species of mustards, common lambsquarters, hedge bindweed, field bindweed, cucurbits, different species of clover and vetch, beans, broad beans, lima beans, lupine, pea soybean, ground Ivy, healall, okra, purslane, pimpernel, black nightshade, pepper, tomato, petunia, eggplant, potato, garden pansy etc. 
 
Cucumber mosaic virus (CMV): pigweed, horseweed, oxeye daisy, coffee weed, Canada thistle, bull thistle, hairy galinsoga, Jerusalem artichoke,  prickly lettuce, wild chamomile, hawkweed, groundsel, Canada goldenrod, sowthistle, endive, sunflower, lettuce, mustard, radish, chickweed, lambs quarters, morning glory, cucurbits, common teasel, alfalfa, beans, lima beans, mung beans, geranium, ground Ivy, okra, purslane, jimsonweed, ground cherry, horsenettle, black nightshade, pepper, tomato, petunia, eggplant, potato, burning nettle, garden pansy. 
 
Lettuce mosaic virus (LMV): lettuce, bristly oxtongue, spinach. 
 
Bidens mottle potyvirus: lettuce, endive, horseweed, hairy beggarticks, virginia pepperweed, Mexican pricklepoppy. 
 
Celery mosaic virus (CeMV): Celery, giant hogweed
 
Papaya ringspot virus (PRSV): Bur cucumber, creeping cucumber, balsom pear, cucumber, cantaloupe, watermelon, summer squash, pumpkin, gourd, winter squash, butternut squash, 
 
Tomato spotted wilt virus (TSWV): Tomato, potato, pigweed, hairy beggarticks, oxeye daisy, coffeeweed, prickly lettuce, annual sowthistle, ebdive, sunflower, lettuce, shepherd’s pruse, chickweed, hedge bindweed, cantaloupe, muskmelon, bean, broad bean, mung bean, cutleaf evening primerose, broadleaf plaintain, purslane, jimsonweed, bittersweet nightshade, black night shade, pepper, tomato, petunia, eggplant, potato. 
 
Tobacco mosaic virus(TMV):  White campion, jimsonweed, pepper, tomato, tobacco. 
 
Turnip mosaic virus(TurMV):  pigweed, wild carrot, bachelo’s button, Canada thistle, hairy galinsoga, smallflower galinsoga, common catsear, pineapple weed, dandelion, endive, sunflower, lettuce, mustard, brassicae crops, corn cockle, chickweed, common lambsquarter, spinach, cucumber, alsike clover, lupine, redstem filaree, ground Ivy, okra, velvetleaf, common pokeweed, purselane, jimsonweed, black nightshade, tomato, petunia..
 
Watermelon mosaic virus (WMV) :   mustard, common lambquarters, spinach, cucumber, watermelon, cantaloupe, squash, buttercup, red clover, common vetch, alfalfa, beans, lupine, pea, henbit, common mallow, okra, common pokeweed, jimsonweed, nightshade, 
 
Zucchini yellow mosaic virus (ZYMV) : cucumber, cantaloupe, watermelon, squash, zucchini, pumpkin, gourds. 
 
 
Source: Cornell.edu

Mark C. Siemens Vol. 12, Issue 20, Published 10/06/2021 Plans are shaping up for the 2nd Automated Weeding Technologies Field Demo Day. The event will be held Thursday, October 21st at the Yuma Agricultural Center. Registration begins at 7:00 am and the program starts at 7:30 am. We have eight presentations/field demos scheduled (details below). The focus this year is on the latest automated weeding technologies that are “new” since our 2018 event. We would love to showcase as many innovations as possible and it’s not too late to be added to the program. It’s an open invitation - private companies, university and government researchers are all welcome to show their technology. Please contact me if you are interested or know someone that is.

Because there are so few selective herbicides registered for use in lettuce, it is necessary to kill as many weeds as possible prior to planting. Fumigants, flooding and solarization will kill weed seeds but it will be necessary to germinate them first for most herbicides to be effective. Almost any herbicide can be used preplant that is registered for “fallow” conditions as long as the preplant and preharvest intervals are observed. The following table summarizes the most commonly used herbicides for ground preparation in lettuce.

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts peaked about 2 weeks ago, but declined areawide this week. About average for October.
 
Beet armyworm:         
Trap counts increased in most locations, but remain well below average compared to previous years.
 
Cabbage looper:          
Cabbage looper up in most traps, particularly active in Yuma Valley and Wellton. About average for this time of season.
 
Diamondback moth:      
DBM moths peaked about 2 weeks ago (Dome and Wellton); below average for this time of the year.
 
Whitefly:                      
Adult movement increased in the past 2 weeks, particularly in areas near melons but remains below average for this time of year. 
 
Thrips:                           
Thrips adults increased markedly in many locations (Tacna, Dome, Yuma Valley), and currently about average for October.
 
Aphids:                        
Aphid movement beginning; light numbers in North Yuma Valley and Tacna. Below average for October.
 
Leafminers:                  
Adult activity up in a few locations (Yuma Valley), below average for September.