It’s hard to believe that it’s been 10 years since the bagrada bug first invaded Yuma produce crops. In 2010, the pest was found in great abundance throughout the desert southwest, causing significant economic damage to large acreages of cole crops.  However, in the past four years bagrada populations have been almost non-existent in our experimental plots (see graphs below) and just as scares in commercial crops. We are not certain why this has occurred but may likely be a combination of good insect management and a little help from mother nature.  However, we did observe an abundance of adults and nymphs colonizing mustard plots this past April.  Thus, I wouldn’t completely count them out this season; a lot will depend on how well they survived the long summer, and if there are any hitchhikers on transplants.  The good news is that so far there have no reports of bagrada showing up on early transplants in Yuma, Coachella or Imperial Valleys.  Further, there have been no reports of bagrada causing problems on coast cole crops.  Experience over the past nine years has shown us that peak adult bagrada bug abundance in the desert generally occurs on direct seeded and transplanted brassica crops in early September.   Research conducted on untreated broccoli and cauliflower plots at YAC have shown that mid-September has historically been the time that bagrada begin to show up in large numbers; peak abundance of bagrada bug has occurred from late September to early October (see graphs below).   These peak occurrences appear to coincide with the end of the monsoon season and the much-reduced humidity.  However, it’s been difficult to observe this effect lately since there has been a trend of significantly lower bagrada bug abundance since 2014 and last the two seasons have been the lightest bagrada populations since we started tracking them in 2010. 

 

So, what should a PCA expect for this season?   We have not had much of a monsoon, and the lower humidity could play to their advantage. We can’t say for sure when they will show up and in what numbers but keep your eyes open for adults on your early plantings.  Here are a few management tips to consider.  (1) When monitoring for bagrada bugs, PCAs should look mainly for fresh feeding signs on new plant tissue, and adults later in the day when they are most active.  (2) Direct-seeded and transplanted crops are susceptible to bagrada bug infestations during stand establishment and up to the 6-leaf stage. After that, bagrada rarely cause damage to head forming brassicas (ie., broccoli, cabbage, cauliflower). Leafy brassicas like kale are much more susceptible to cosmetic damage throughout the season though.  (3)  We recommend that control be initiated immediately if you can readily find 5% or more of plants with fresh-feeding signs. This can include chemigation or aerial applications with pyrethroids. Contact insecticides such as pyrethroids, Lannate, and Lorsban should be used once stands are lined out.  Once pipe is pulled and plant size increases up to the 2-3 leaf stage, or on tagged transplants, consider alternating to foliar dinotefuran (i.e., Scorpion) sprays for protecting plants from bagrada feeding. This neonicotinoid will also provide knockdown of adult whiteflies and nymphs.  (4)  Also, growers who plant Nipsit broccoli seed (clothianidin treated) should begin to closely monitor for fresh feeding damage around 14 days after emergence.  More information on bagrada bug management on fall cole crops can be found in:    Bagrada Bug Management Tips for the Low Desert 2019.

 

 

 

Can you ID the insect below?

When 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 yield potential, and 3) anticipate the next stage of development and what we need to do in terms of field crop management.  These considerations are commonly focused on aboveground crop evaluations.  However, the root system is also an extremely important part of the crop condition to evaluate.  
 
Root systems were described in a basic manner in a recent article on 2 May 2023 (UA Vegetable IPM Newsletter Volume 14, No. 9).  
 
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 and nutrient uptake by plant roots takes place in the top 24 inches of the root zone; about 20% from the third quarter; and about 10% from the soil in the deepest quarter of the root zone (Figure 1).  
 
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.

Figure 1.  General pattern for plant-water and nutrient uptake from the soil profile. 

It is important to point out that these general root development patterns are dependent on the nature of the soil profile in the fields.  Soil profiles with compaction layers, as well as rock or caliche layers will limit root development and full exploration of the soil volume that the plants are capable of (Figure 2).

Figure 2.  Generalized soil profile with major horizons.

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 to be careful of where and how we sample plants and the root systems in a field.
 
Crop species can vary significantly in their patterns of root development and it is important to know what is “normal” when evaluating crops in the field.  An excellent reference for vegetable crop root system development is a 1927 publication by Dr. John E. Weaver and William E. Bruner from the University of Nebraska (Root Development of Vegetable Crops).  This publication can be found at the following link:
 
https://soilandhealth.org/wp-content/uploads/01aglibrary/010137veg.roots/010137toc.html
 
A few basic examples from the Weaver and Bruner publication are provided in the following figures (Figures 3-10).

Figure 3.  Cauliflower, 3 weeks after transplanting.



Figure 4.  Cabbage roots, 55 days after transplanting.



Figure 5.  Cabbage roots, 75 days after transplanting.



Figure 6.  Pepper roots, 24 days.



Figure 7.  Pepper roots, 45 days (6 weeks).



Figure 8.  Pepper roots, mature.



Figure 9.  Lettuce roots, 3 weeks.  The roots on the right were grown in compact soil, the roots on the
left were grown in loose/open soil.



Figure 10.  Lettuce roots, 60 days.

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

It’s October and planting season is well underway. When planting lettuce, uniform seed spacing is critical for efficient, economical crop thinning. Due to their lack of precision, automated lettuce thinning machines cannot eliminate lettuce plants that are spaced closer than about 1 1/8” apart. These closely spaced plants, commonly referred to as “doubles”, must be carefully removed by hand which is time consuming and expensive.

Several years ago, we conducted trials examining the influence of planter travel speed on seed spacing uniformity (Siemens and Gayler, 2016). In the study, two types of planters - a vacuum planter (Stanhay 785 Singulaire) and a belt planter (Stanhay 870) were tested with pelleted lettuce seed at travel speeds of 1.0, 1.5, 2.0 and 2.5 mph at the Yuma Agricultural Center. Vacuum planter test results showed that the percentage of “difficult to thin” spacings, defined seeds spaced less than 1.1” apart, increased from about 5% to 10% as speed increased from 1.0 mph to 2.5 mph (Fig. 1). Concomitantly, the percentage of seeds “precisely placed” within 0.5” of the target location (i.e., 2.0 ± 0.5”) decreased from 70% to less than 45%, and the percentage of skips increased from 7% to 30%. Variability of seed spacing uniformity as measured by the coefficient of variation (COV) of seed spacings also increased.

Similar declines in planter performance were found with the belt planter (Fig. 2). As travel speed increased from 1.0 to 2.5 mph, the percentage of difficult to thin spacings increased from 2% to 10%, precise spacings decreased from 93% to 65% and skips increased from 2% to 8%.

For both planter types, there was a significant decline in performance as speed increased from 1.5 mph to 2.0 mph, a difference in speed of only 0.5 mph. These results suggest that it is prudent to check planter performance at the chosen operating speed prior to establishing an entire block to ensure that seed spacing uniformity, not just the number of seeds per foot, is acceptable.

In short, the study showed that planter travel speed had a significant effect on seed spacing uniformity and difficult to thin, close spacings - the higher the speed, the poorer the performance.

You may be asking what is the reason for the phenomenon observed? A logical explanation is that seeds are traveling at the speed of the planter when they are released and tend to “bounce and roll” in the direction of travel when they hit the soil surface. Thus, the higher the travel speed, the further seeds bounce and roll resulting in increased seed spacing variability.

References

Siemens, M.C., & Gayler, R.R. (2016). Improving seed spacing uniformity of precision vegetable planters. Appl. Eng. Agric., 32(5), 579-587

Fig. 1. Seeding performance of a vacuum vegetable planter sowing lettuce when
operated at four travel speeds.


Fig. 2. Seeding performance of a belt vegetable planter sowing lettuce when operated at
four travel speeds

Sprinkler irrigation systems are delivering water throughout the Yuma CO. Either for germination or chemigations in lettuce, broccoli, onion and spinach.
How are you handling the absence of Dacthal (DCPA) in your operations?
One strategy that worked good in onions at the Gila Valley for one of our PCAs this week was the application of Prefar (bensulide) at 6qt. The weed complex he has included Purslane (Portulaca oleracea), Pigweed (Amaranthus palmeri), and is expecting later germination of Lambsquarter (Chenopodium album), Gooseofot (Chenopodium murale), and London Rocket (Sisymbrium irio). Control looks great and scouting the field in untreated areas we noticed there was a seedbank that could have caused a problematic infestation of purslane. The Pest Control Advisor is planning to include Goal (oxyfluorfen) in his weed control program later. 
We all know bensulide is an old treatment and many of you are using it, but our friend PCA wanted to share his experience just in case some of us have the same weeds.
If you would like to share with the Ag. community some of your experiences or new strategies used successfully, email the IPM Team. Also, please let us know if you like include a treatment or see a product tested in the onion and broccoli herbicide trials we are starting at the Experiment Station.
 
Following are links to some articles on onion weed control:
 
https://ag.arizona.edu/crop/vegetables/weeds/Dacthal.html
 
https://escholarship.org/content/qt91w4d06x/qt91w4d06x.pdf?t=lnryxp&v=lg
 
https://repository.arizona.edu/bitstream/handle/10150/221477/370100-165-167.pdf
 
https://ipm.ucanr.edu/agriculture/onion-and-garlic/herbicide-treatment-table/

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.

Leaf miners: Adult activity light in all areas, about average for this time of season