May 4, 2022Spider Mites on Spring Melons 2022To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Arizona agriculture utilizes ~ 70% of the water in this state and generates a strong and productive industry. Arizona agriculture generates more than $23B in sales as well as directly and indirectly supporting more than 138,000 Arizona jobs and employing more than 162,000 unique workers. Arizona ranks among leading states in the production of lettuce, spinach, broccoli, cauliflower, cantaloupe, honeydew melons, durum wheat, and other commodities. Arizona is an important area for the seed production of many crops that are used across the U.S. and worldwide. Many Arizona counties rank in the top 1% of all U.S. counties in terms of crop and livestock production (Murphree, 2018).
In response to the Colorado River (CR) water shortage and the current reductions in CR allocations to Arizona via the Central Arizona Project (CAP), which is primarily impacting agricultural irrigation districts in central Arizona, there is an increasing level of scrutiny on agricultural uses of Arizona water. This of course is accentuated with the recognition that agriculture utilizes ~ 70% of the Arizona water supply.
In the irrigation districts along the mainstem of the CR, there is a common adage of “First in use, first in right.” This is a fundamental aspect of the “law of the river”, which is an amalgam of the various laws, agreements, and rulings on the governance of CR water. Therefore, it is important for us to consider and prepare the positive case that can be made for the good stewardship of water resources provided by Arizona agriculture.
One common area of criticism that is directed towards Arizona crop production systems, is the use of surface and flood irrigation systems. The alternative irrigation methods that are commonly advocated for use instead of flood irrigation are methods such as drip irrigation, micro-irrigation systems, sprinklers, etc. Each of these are good irrigation methods and advantageous under the appropriate conditions. However, a good case can be made for the very efficient use of flood irrigation systems, particularly with high-flow turnouts and dead level (or very nearly so) basins for irrigation. When properly managed, these types of flood irrigation systems can be very efficient.
When we know the area to be irrigated, the flow rate of water in the irrigation delivery ditch, and the amount of water needed; then we can determine the proper time or duration for an irrigation event. If we can get fast and uniform coverage of the field to be irrigated, apply the proper volume of water to replenish the plant-available water supply to the soil, then cut off the flow of irrigation water into the field; we can do a very good job of delivery for high water-use efficiency.
To facilitate the process of managing individual irrigations for optimum efficiency, the Irrigator’s Equation can be used to estimate the depth of water applied or time (duration) of an irrigation event.
Q x t = d x A
Where: Q = the flow rate, in cubic feet per second (cfs);
t = the set time or total time of irrigation (hours);
d = the depth of water applied (inches) and
A = the area irrigated (acres).
With an understanding of the dominant soil type in the field being irrigated and the level of soil-water depletion at the time of irrigation, we can estimate the amount or depth of water needed to replenish the soil profile of plant-available water to support the crop and prevent water stress.
In managing crop fields and irrigations, we recognize that soil textures vary in terms of water holding capacities and it is important to understand the dominant soil textures in the field, not only on the surface but also through the depths of the soil profile through the effective rooting depth of the crop, Tables 1 & 2.
Collectively, we can manage surface or flood irrigation systems efficiently. In the crop production arena, it is important to communicate these points effectively.
Table 1. Soil texture and water holding capacity.
2. Depths to which the roots of mature crops will deplete the available water supply when grown in a deep permeable, well-drained soil under average conditions.
Source: Chapter 11, "Sprinkler Irrigation," Section 15, Natural Resources Conservation Service National Engineering Handbook
Murphree, J. 2018. Arizona Agriculture is 23 Billion Dollars Beautiful, Arizona Farm Bureau.
Botrytis rot is not considered a major problem in lettuce but it can cause significant damage/loss when the field conditions are favorable for the pathogen. Cool wet conditions are favorable for the pathogen. Symptoms include water-soaked, brownish-gray to brownish-orange, soft wet rot that occurs on the oldest leaves in contact with the soil. Old leaves are more susceptible than young leaves and the fungus can move into the healthy parts. Fuzzy gray growth can be observed in the disease area which is characteristic of the pathogen. In worse cases, the entire plant can collapse. Romaine cultivars, transplanted lettuce that are big and have leaves touching the soil are more susceptible.
The pathogen: Botrytis cinerea
Botrytis cinerea affects most vegetable and fruit crops, as well as a large number of shrubs, trees, flowers, and weeds. Outdoors Botrytis overwinters in the soil as mycelium on plant debris, and as black, hard, flat or irregular sclerotia in the soil and plant debris, or mixed with seed. The fungus is spread by anything that moves soil or plant debris, or transports sclerotia. The fungus requires free moisture (wet surfaces) for germination, and cool 60 to 77 F, damp weather with little wind for optimal infection, growth, sporulation, and spore release. Botrytis is also active at low temperatures, and can cause problems on vegetables stored for weeks or months at temperatures ranging from 32 to 50. Infection rarely occurs at temperatures above 77 F. Once infection occurs, the fungus grows over a range of 32 to 96 F.
Masses of microscopic conidia (asexual spores) are produced on the surface of colonized tissues in tiny grape-like clusters (see picture). They are carried by humid air currents, splashing water, tools, and clothing, to healthy plants where they initiate new infections. Conidia usually do not penetrate living tissue directly, but rather infect through wounds, or by first colonizing dead tissues (old flower petals, dying foliage, etc.) then growing into the living parts of the plant.
1. Buy high-quality seed of recommended varieties. Treat the seed before planting.
2. Practice clean cultivation. Plant in a light, well-drained, well-prepared, fertile seedbed at the time recommended for your area. If feasible, sterilize the seedbed soil before planting, preferably with heat. Steam all soil used for plantbeds at 180 F (81 C) for 30 minutes or 160 F (71 C) for one hour.
3. Avoid heavy soils, heavy seeding, overcrowding, poor air circulation, planting too deep, over-fertilizing (especially with nitrogen), and wet mulches.
4. Focus on healthy plant vigor. Do not over fertilize.
5. Use drop or furrow irrigation instead of sprinklers. If sprinklers have to be used, irrigate morning or early afternoon giving enough time for foliage to dry.
6. Apply recommended fungicides when conditions favor disease development. Make sure to rotate fungicide to avoid development of resistance.
Vol. 13, Issue 4, Published 2/23/2022
Keeping up to date with the latest developments in automated weeding machines is challenging. It’s a very fast-moving space with significant private and public investment. At the 2022 Southwest Ag Summit “Innovations in Weed Control Technologies” breakout session, university experts and cutting-edge innovators will provide updates on the latest domestic and international developments in automated weeding, autonomous ag robots, and non-chemical weed control (agenda below). The session will be held TOMMOROW Thursday, February 24th from 1:30-3:30 pm.
As I mentioned in the last newsletter, we’ll also be demoing our band-steam applicator for controlling soilborne diseases and weeds at the Southwest Ag Summit Field Day. We’ll also have our 2nd generation prototype band-steam applicator on display (Fig. 2). It is simpler in design and has a higher capacity steam generator as compared to our first prototype. This will increase travel speed and thereby work rate. The event is scheduled for TODAY, Wednesday, February 23rd from 10:30 am – 4:30 pm.
For more information about the Southwest Ag Summit, visit https://yumafreshveg.com/southwest-ag-summit/.
Hope to see you there!
This work is partially funded by the Arizona Iceberg Lettuce Research Council, Arizona Specialty Crop Block Grant Program and USDA-NIFA Crop Protection and Pest Management Program.
Fig. 1. “Innovations in Weed Control Technologies” breakout session agenda at the 2022 Southwest Ag Summit. Session will be held Thursday, February 24th at Arizona Western College, Yuma, AZ.
Fig. 2. Prototype band-steam applicator for controlling soilborne pathogens and weeds on display at the 2022 Southwest Ag Summit, Yuma, AZ. Applicator sled and trailer fabricated by Keithly-Williams Fabrication, Yuma, AZ. Steam generator provided courtesy of Simox, Contamine-sur-Arve, France.
Clovers can be very difficult to control weeds here, but it is also a major crop and common ornamental. Clovers can survive under poor growing conditions and are not controlled with glyphosate and seem to get worse every year. There are more than 50 types and 300 species of clover and they can be easily misidentified. They are all in the legume (Fabracea) family and can use a bacterium (rhizobium) in the soil to convert nitrogen in the atmosphere to a form that they and other plants can use for fertilizer. There are only 4 or 5 clover species that are agricultural pests here. The ones we get the most questions on are white and yellow sweet clover. These are in the Melilotus family. White sweet clover (Melilotus albus) is tall for a clover and can get 3 to 5 foot in height. The leaves are thinner than most clovers and this difficult to control weed lives at least 2 years and sometimes longer. Glyphosate and most of the contact herbicides do not control it. The plant growth regulator herbicides work best. Yellow sweet clover (Melilotus officinalis) is less common here. The flowers are yellow, and it is not as tall and vegetative as white sweet clover. Yellow is more common at higher elevations. California burclover (Medicago polymorpha) and Black medic (Medicago lupina) are in the same genus as alfalfa and are more of a problem in landscapes, parks and golf courses than in agricultural fields here. They do not grow upright and spread below the crop or turf. The true clovers are in the Trifolium genus and include white and strawberry clover. These creep along the ground and root at the nodes of the stem. These are more of a urban landscape weed and not considered an agricultural problem. Creeping woodsorrel or Oxyalis looks like a clover but it is not related. It is a turf weed that spreads rapidly along the ground and can live for several years. Preemergent herbicides are effective against all these clovers before they become established. The postemergence herbicides that are most effective in controlling these clovers are the plant growth regulators. Contact herbicides and glyphosate are generally ineffective.