May 4, 2022Spider Mites on Spring Melons 2022To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
This season we have already found few lettuce infected with bacterial soft rot. Though it rarely takes down the whole field, the symptom are not so pleasant. Bacterial soft rot in lettuce can occur in the field as well as post harvest.
It is caused by several types of bacteria, but primarily subspecies and pathovars of Erwinia caro-tovora and E. chrysanthemi. Other bacterial species that cause soft rot include Pseudomonas cichorii, P. marginalis, and P. viridiflava. They have a wide host range host range and includes genera from nearly all plant families
In lettuce fields, the symptoms are observed close to the harvest time. The tissue, mostly around inside the head of head lettuce softens and becomes mushy or watery. Slimy masses of bacteria and cellular debris frequently ooze out from cracks in the tissues. Decaying tissue, which may be opaque, white, cream-colored, gray, brown, or black frequently gives off a characteristically putrid odor. The odor is caused by secondary invading bacteria
that are growing in the decomposing tissues.
The bacteria overwinter in infected fleshy tissues in storage, in the field, garden or greenhouse, in the soil (especially in the rhizosphere around the roots of many plants), and on contaminated tools, equipment, containers, and in certain insects. The bacteria enter primarily through wounds made during planting, cultivating, harvesting, grading, and packing and through freezing injuries, insect and hail wounds, growth cracks, and sunscald. They may
also follow other disease-producing organisms. Uninjured tissues may become infected when the humidity approaches 100 percent or when free moisture is present. Rains, poorly drained or waterlogged soils, and warm temperatures favor infection in the field, as does high humidity in storage or transit.
The bacteria multiply rapidly by dividing in half every 20 to 60 minutes under ideal conditions at
temperatures between 65° and 95° (18° and 35°C). Minimum temperatures for development is between 35° and 46°F (2° and 6°C); and maximum between 95° and 105°F (35° and 41°C.
The bacteria are spread by direct contact, hands, tools and farm machinery, insects, running or splashing water, contaminated, water in washing vats, clothing, and decayed bits of tissue.
Promptly and carefully destroy infected plants. Maintain well aerated field, avoid close planting and overhead irrigation.
To minimize post harvest losses, avoid mechanical injusry after harvest, packing and shipping. Do not pack produce when wet. Store and ship produce at temperatures near 4°C (39°F).
It’s October already and soon crews will be thinning and weeding vegetable crops in the Yuma area. Automated machines for performing these tasks are commercially available and being used more and more. Due to significant research and development efforts being made in this area, the technology used for these machines is advancing rapidly. In the next series of articles, I will be discussing the developments made over the summer by automated machine manufactures and what growers in the Yuma area can expect for the upcoming season.
The first technology I’d like to discuss is the autonomous weeding robot “Dino” manufactured by Naïo Technologies (Fig. 1). Briefly, the robot is an 84” wide, self-piloted, mobile power unit equipped with camera guided cultivating tools.
Last season, Naïo demoed the robot for growers in the Yuma area. It was the first year the French based company had operations in the U.S. One goal of the demonstrations was to evaluate the machine in U.S. conditions and get feedback from growers about how the machine might best fit Arizona production systems. The company learned that Arizona vegetable production is very intense and fast paced. Machine productivity and durability were important issues for viability and domestic acceptance.
The company took heed of these observations. Over the summer, the battery that powers the fully electric robot was upgraded to provide 10 hours of operation before needing to be recharged. This improved work capacity from 8 acres/day to about 10 acres/day (work rate = ~ 1 acre/hour). To further address the capacity issue, the company imported three additional machines so that multiple machines could be operated simultaneously in the same field. The new machines are more robust, being equipped with higher torque drive wheel motors and a sturdier frame. The company is also in the process of switching to an improved camera guidance system that should enhance crop tracking ability and close cultivation performance. Some may be aware that the company has developed an award winning active in-row weeding tool that cycles cultivating blades in and out of the crop row (Link). The device is undergoing further testing and is planned for commercial release in mid-2021.
Machines will be available this fall in the Yuma area for demos or for hire as a weeding service. It will be interesting to see how these advanced robots perform and benefit weed management. If you would like assistance evaluating these machines or conducting performance trials, please feel free to contact me.
 Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.
Heavy and widespread infestations of common purslane come up during ground preparation for lettuce every year. This occurs in fields that were kept weed free the previous year and is difficult to understand.
There are probably several reasons for this.
Common Purslane is very prolific. It has been reported that one plant can produce up to 240,000 seeds. The stems are so succulent that plants can remain viable and make seed even after it is uprooted.
Once seed is mature it can be viable for as long as 40 years. It has very small, hard seed that can remain dormant in the soil for ss long as 40 years .So you may have to control weeds that got into the field a generation ago..
Multiple perennial germinations
Common Purslane is supposed to be a summer annual, but it germinates multiple times all year in the low desert. It takes 12 hours after receiving moisture in the summer and 7 days in the winter, but it keeps germinating. It has to be controlled when it is less than 2” in diameter. If you wait until most of it germinates the early plants will be too big. If you spray or cultivate when all the emerged plants are small you will miss many that have yet to emerge. It is best to treat early and control the later emerging plants with a selective herbicide.
When common purslane is broken in pieces it can reroot at the nodes. Late cultivation often spreads this weed. Cultivation is not a good option when purslane is larger than 2”. Herbicides are a better option on big plants.
Purslane has a very small light seed. It moves in irrigation water and blows in the wind. Even completely clean fields are likely is be reinfested by seeds that are carried by water and wind into the field.
Considering the above factors, the best option for controlling common purslane may be preirrigation to germinate the weeds and early herbicide application or cultivation . Kerb and Prefar are both good on purslane. Prefar should be used at planting to incorporate it with a lot of water and Kerb should be used later to avoid leaching but don’t wait too long and risk germination of the weeds. Purslane germinates from shallow depths and split applications of Kerb may be a good option.