Jan 24, 2024Avoid Seed Corn Maggots in Spring Melons (2024)To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
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:
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.
Late blight of celery is caused by fungi Septoria spp. The disease is named late blight as it is mostly seen at the later in the growing season but don’t be surprised if you see the symptoms in early season when the weather is conducive. With the rain and fog we had this week, it is possible that we get this disease in celery this growing season. Leaf spots are dark, circular to irregular in shape, and 3-10 mm in diameter. Dark colored fruiting bodies (pycnidia) of the fungus which form in the center of leaf spots give the spots a grainy appearance. In case of severe infection, large number of spots are formed and can significantly reduce yield. Sometimes, angular spots are seen as the symptoms are restricted by leaf venation. The stalk or petiole of the plants can also be infected and large number of pycnidia observed in the stalk. Pycnidia is basically huge amounts of asexual spores in dark fruiting bodies and are formed on the older lesions and their development is encouraged by moist weather.
The pathogen is seed borne but will survive in soil in decomposing celery tissue for months. Cool and wet weathers favor the disease. Temperatures below 75 F are conducive to disease formation. High humidity allows abundant production of spores and epidemics are initiated by splashing spores or by movement of spores by contact. Rain, heavy dew or fog, and sprinkler irrigation when temperatures are above 70°F encourage disease development; splashing water disperses spores and aids in spore germination and infection
Acquiring clean seeds is the best management practice for the disease. Hot water treatments are effective but might interfere the germination percentage. Clean cultivation, not planting new crop next to the infected crop field, crop rotation, and fungicides can be used to manage the disease. Avoid sprinkle irrigation after symptoms are observed. Copper sprays can be used in organic farming.
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.
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