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.

This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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, which contained two 25 ft rows of lettuce. Plants were thinned on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

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.