It’s never too early to start planning for next produce season. And this includes maintaining a clean culture with effective weed control.  I think most PCAs and growers recognize that weed management is important in leafy vegetable and melon production for all the obvious reasons.  However, weed management is also essential for another important, but often overlooked, reason.  Weeds can serve as host plants for many important insect pests, and when not controlled in the field they can be an impediment to insect control. Weeds can serve a beneficial role by harboring insect natural enemies and pollinators, but the consequences resulting from weeds harboring insect pests often outweigh benefits they potentially provide.   Although flowering weeds can provide a reservoir for natural enemies, and a source of nectar and pollen for a pollinators, these same weedy refuges can serve as host sources for many key insect pests that cause economic damage to vegetable crops.  Weeds found on field margins and ditch banks can provide insect pests with suitable resources needed for rapid population growth which subsequently can lead to insect infestations occurring in adjacent vegetable crops.   In addition, many weed species can provide insects with host plants that serve as a bridge between cropping seasons when vegetables crops are not in production (May-August).  Volunteer melons and cotton are also considered weeds (“a plant out of place”). If not removed in a timely manner, these weedy volunteer plants can sustain large numbers of insect pests that can disperse onto newly planted fields.  Weeds can also serve as alternate host plants for three important groups of viruses that affect vegetable and melons; tospoviruses, potyviruses and criniviruses.  For example, one of the primary insect vectors of the crinivirus Cicurbit Yellows Stunt Disorder Virus (CYSDV) is the sweetpotato whitefly.  Not surprising, common desert weed species such as alkali mallow, groundcherry, pigweed, lambsquarter, London rocket, and silverleaf night can all harbor large whitefly numbers  and serve as reproductive hosts. More importantly, these weeds are known reservoirs of CYSDV.   Finally, weeds can serve as impediments to insecticide applications.  Dense weed foliage in vegetable and melon fields can negatively influence foliar spray applications by intercepting spray droplets before reaching the crop, which can result in less insecticide deposition and unacceptable crop damage.  Soil applied systemic insecticides (e.g., imidacloprid, Coragen, Verimark) can also be impacted by unmanaged weed growth. Weeds growing unchecked during stand establishment can compete with the seedling plants for water and fertilizer, but they can also compete with crop plants for soil insecticides. Excessive weed densities can significantly intercept insecticides in the soil profile and reduce the amount available for uptake by the target crop.   For more information on this topic, please visit Weed Interference with Insect Management in Desert Crops.

Crops need to be monitored during all stages of growth to best manage water and nutrient inputs.  Taking crop condition into account and adjusting nutrient and water management accordingly is critical in achieving the optimum management of a crop and the best use of an irrigation system and fertilization program.  This is often referred to as a “feedback” system of crop management (Silvertooth, 2001).  This concept and approach to crop management can perhaps be most useful with an irrigated crop production system.  Irrigated chile (Capsicum annuum L.) production in the desert Southwest is a good example and it demonstrates the benefits in crop management when coupled with a fundamental understanding of crop phenology (growth and development). 

Increased efficiency is an important objective for developing sustainable chile crop production systems.  Efficiency can be defined in economic (return on the investment), agronomic (crop system response), or environmental (impact on environmental quality) terms.  Each of these concepts of efficiency can be successfully addressed simultaneously, which requires good management and attention to the changes that take place over the growth cycle of a crop.

When monitoring any crop in a production system there are several factors that are very important to consider including: 1) stage of growth, 2) crop vigor, and 3) yield potential.  A feedback system of management can be useful in adjusting critical crop inputs such as water and fertilizer inputs (particularly N) in response to actual crop conditions.  For example, in the case of irrigated chile, if the crop is experiencing poor vigor and symptoms of stress, it would be very important to identify the source of the stress and make an effort to address or correct it.  This could relate to several issues such as pest infestations (insects, weeds, or diseases), water stress, salinity stress, nutrient deficiency, etc.  If for example a crop is experiencing poor vigor due to water stress, the application of additional N will not be effectively utilized by the crop until the water stress situation is adequately addressed.  Alternatively, if a chile crop is experiencing very high vigor and excessive vegetative growth (often accompanied by a poor fruit load), a more conservative approach with N inputs would be warranted and at the same time it would be important not to impose a water stress per se.

Thus, monitoring a chile crop production system and having a gauge on basic factors such as stage of growth and the plant relationships to water and nutrient requirements are essential in realizing optimum efficiency regarding irrigation and fertilization inputs.  Flexibility in management is required to better respond to the crop and production conditions that can change quite rapidly during a production season and will vary from season to season.  Accordingly, managers need to be flexible in managing the system in response to the appropriate queues to realize the full potential from a crop production system.  This type of agronomic system efficiency is important for both short- and long-term sustainability.

To optimize N management for a chile crop it is important to make fertilizer N applications in the “Nitrogen Application Window” (NAW) described in Figure 1 which provides a baseline for chile growth and development as a function of heat units accumulated after planting (HUAP, 86/55 F thresholds; Brown, 1989; Baskerville and Emin, 1969).   Chile crop phenology as a function of HUAP is described in Extension Bulletin AZ1529 (Silvertooth et al., 2010).  The NAW is positioned just prior to the period peak N demand by the chile crop during the phase of growth when N demand is rapidly increasing after the crowning stage of development.  Nitrogen applications made in this manner in advance of the N demand period increases the probability of fertilizer N uptake and recovery by the plant.  Thus, the NAW extends from the crowning stage to just past peak bloom (~1200 – 2300 HUAP).  

Chile crop water demand also increases quite rapidly during this same period of growth with maximum chile crop water demand occurring from early bloom until the completion of development of the primary pod set (~1600 – 2500 HUAP).  For green chile this peak water demand will extend up to the time of crop harvest.  For red chile, peak water demand declines as the crop transitions from ~ 50% green and 50% red chile on the plants, or the stage that is commonly referred to as the maximum “chocolate chile” stage.

For both water and N management it is important to monitor crop growth and development as well crop condition including vigor, fruit load, etc.  Water stress should be avoided during these stages of growth and N management needs to be flexible in response to changes in crop condition during these peak periods of demand.  Crop monitoring and flexibility are key elements to management for optimum crop production efficiency.

Nitrogen application rates will vary depending on other factors such as residual soil N levels, N concentrations in the irrigation water, previous N fertilizer applications, cropping history for the field and residual crop residues, as well as the current condition of the crop or field in question.  Nutrient uptake studies have shown that approximately 180 lbs. N/acre is the maximum amount of total N required by green and red chile crops for optimum yields.  Actual total fertilizer N amounts needed by an irrigated chile crop usually equate to a total of 100 – 150 lbs. N/acre for the entire season.  However, as previously stated, this rate can vary tremendously depending on actual crop and soil conditions.

Nitrogen management for irrigated chile should be directed to provide the total fertilizer N for a crop within the NAW with split applications toward a maximum target of approximately 100 – 150 lbs. N/acre.  Late season N fertilizer applications can delay crop maturity and harvest.  Crop and soil monitoring in-season is critical to allow appropriate adjustments in N fertilizer applications to best match in-season conditions in the field optimize this important facet of chile crop management.

Figure 1.  Nitrogen (N) application window and maximum water demand period
for New Mexico type chiles in the desert Southwest of the U.S.

References
Baskerville, G.L. and P. Emin.  1969.  Rapid estimation of heat accumulation from maximum and minimum temperatures.  Ecology 50:514-517.
Brown, P. W.  1989.  Heat units.  Bull.  8915, Univ. of Arizona Cooperative Extension, College of Ag., Tucson, AZ.
Silvertooth, J.C. 2001.  Feedback requirements for nitrogen in irrigated cotton.  AZ1201, University of Arizona Cooperative Extension Bulletin.
Silvertooth, J.C., P.W. Brown, and S. Walker.  2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum).  AZ 1529, University of Arizona Cooperative Extension, College of Agriculture and Life Science, Tucson, AZ.

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.

Shallowing steaming soil for weed control in spinach and baby leaf lettuce crops – machine in action and trial results (>89% weed control) video. Watch it here!

Fig. 1. Steam applicator principally comprising a 63 BHP steam generator
mounted on a bed-shaper applicator sled for killing weed seed prior to planting.
Steam applicator injects steam as beds are formed.After cooling (< ½ a day), the
crop is planted into the disinfested soil.

 

When I think about Lipid Biosynthesis Inhibitor herbicides, Post (sethoxidim) and Select (clethodim) come to my mind. A great description of these type of herbicides can be found at the Section VI of the Arizona Pest Control Advisor (PCA) Study Guide. They say a good teacher can explain complicated things in a simple way. Please read this explanation by Barry Tickes:

“These herbicides are known as ACCase inhibitors because they inhibit the production of acetyl-coenzyme A carboxylase (ACCase) which is an enzyme needed in the first steps of lipid or fatty acid production. Lipids are needed in the production of new membranes which, among other things, are needed in the production of cell walls. These chemicals move from the foliage to the growing points, only kill grasses, and have very little soil activity. Grasses stop growing immediately and slowly turn chlorotic or red and die usually in 7 to 21 days. These products are used to selectively kill grasses in broadleaf crops".
 

Classification	Common Name (s)	Commercial names	Arizona crop registrations
Aryloxphenoxy Propionates	fluazifop fenoxaprop clodinafop diclofop	Fusilade Puma, Acclaim, Option, Whip Discover Hoelon	Small grains, Cotton, trees & vines, Several broadleaf crops
Cyclohexanediones	sethoxydim clethodim tralkoxydim	Poast, Segment, Vantage, others Select, Arrow, Prism, Envoy, Intensity, Volunteer, Trigger, Section, others Achieve	Alfalfa, cotton, Several broadleaf Crops Small grains

 
You need to see this .. time lapse photography shows the symptoms of Poast herbicide to wheat.

MOST RECENT Area wide Insect Trapping Network Report   VegIPM Update, Vol. 14, No. 14, Jul 12, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts decreased in the past 2 weeks and about average for this time of summer.
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Valley and Wellton) but about average for July.
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall compared to last season.
 
Diamondback moth:       
DBM moths were not caught in any trap in the past 2 weeks; average for this time of the year.
 
Whitefly:                       
Adult movement continuing to increase, particularly in Gila and Yuma Valleys consistent with melon harvest.
 
Thrips:                           
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent consistent with what we typically see in the summer. 
 
Leafminers:                  
Adult activity has highest in Yuma and Dome Valley, and above average for early July.