Root maggots are serious pest of brassica crops (broccoli and cauliflower, Brassica oleracea var. botrytis) in the Salinas Valley causing widespread economic damage. Maggots are the larval stages of true flies (Order Diptera). In the Salinas Valley, broccoli and cauliflower are grown in 28,328 Ha mostly in rotation with lettuce. Root maggots mostly infest roots (Fig. 1a), but if the population pressure is severe, they could even attack the floret/flower head (Fig. 1b). Cauliflower is a transplanted crop, thus, seedlings are raised in nurseries whereas, broccoli is direct seeded. One of the anecdotal hypotheses among growers and pest control advisors is that the transplants are infested with eggs or maggots prior to planting, thus causing widespread losses.

Method: Plants infested with root maggots were collected from the field during Dec. 2012 to Mar. 2013 and were identified at the species level using dipteran keys. Also, representative samples were identified by an insect taxonomist at California Department of Food and Agriculture. Root samples were collected from seven cole fields (5 cauliflower and 2 broccoli) in the Salinas Valley during Dec. 2012 to Mar. 2013. Each field was broken up into two zones, border and central. Border zone was adjacent to surrounding field/road. A zone consisted of two beds. Number of healthy plants was qualified per zone and the percent plant mortality was determined. Within each zone, 100 root samples were randomly collected and were examined for root maggot infestation.

Results and Discussion: Root maggots sampled from infested-broccoli, cauliflower, and turnip fields in the Salinas Valley of California were cabbage maggot, Delia radicum (L.). Location of the fields positively identified as infested with cabbage maggot is shown in the Figure 2. The plant mortality tended to be more common in the border than in the central zone of the cole fields (Fig. 3). This result suggests that cabbage maggot infestations have been most likely related to invading flies from the surrounding fields than pre-infested transplants. I will continue monitoring the root maggot species on brassica and pattern of infestation in the Salinas Valley.

Recently in the Salinas Valley, subterranean springtails (Family: Onychiuridae) have emerged as a serious pest of lettuce. These soil dwelling primitive insects primarily attack germinating lettuce seeds and young plants, reducing the plant vigor or cause death, which cause patchy or area-wide stand loss. Most springtails possess a forked organ (furcula) in the rear-end, which is extended forward and backward to jump (Fig. 1); hence, the common name, springtail. However, the springtail species, sampled from lettuce fields causing the stand loss, does NOT have furcula. This means they cannot jump. This springtail species is about 3 mm long, wingless, totally blind, possess 3 pairs of legs and short 4-segmented antennae and white/off-white in color (Fig. 2). Mouth parts of the springtail are mostly hidden within the head.

Springtails are generally considered as beneficial insects because they aid in the decomposition of the soil organic matter by feeding, which in turn improves soil health or structure. In addition, these insects feed on the soil dwelling fungal hyphae and spores. In the Salinas Valley, the cool weather in the spring slows the seed germination and decomposition of plant residues incorporated in the previous season (December).

The slow seed germination or seedling growth, presence the ample organic matter, and sufficient soil moisture are the perfect recipe for rapid reproduction, leading to an outbreak in population of springtails. It is important to note that these insects are less affected by the cooler weather in the spring. This indicates that the slowly germinating seeds or tender plant tissue are likely vulnerable to being attacked by the sheer number of springtails in a given area.  

It is likely that these white springtails are easily mis-identified as symphylans because of white color, tiny, and lack the ability to jump. Symphylans are NOT insects but centipede-like organisms. Unlike symphylans, which move into deeper profiles of the soil, springtails remain active in the top layer of the soil, provided sufficient moisture is present. Springtail population crashes once the top soil layer does not have sufficient moisture because they hardly move to lower depths of the soil profile. Symphyans are also white in color, but are highly mobile; possess 10-12 pairs of legs, and multi-segmented antennae (Fig. 3).

Monitoring for springtails is the key to determine presence and size of the population. It is suggested to deploy 4-8 potato or beet-root slices to detect presence of springtail before seeding at least 50 meters apart in the field. Although this technique is used to detect symphylan activity in the soil, it has been observed that these subterranean springtails are also attracted to potato or beet-root slices. Place the potato or beet-root slices after gently racking the surface soil and cover it with a bowl then put soil over it. After 2-3 days, check the slices for springtails. Preliminary data suggest that timing of insecticide application could reduce the stand loss. If the springtails are detected during the pre-seeding period on the potato slices, insecticide applications before seeding and/or at seeding could suppress the springtail populations to reduce stand loss. However, incidence of very high springtail populations at certain patchy areas may not get completely suppressed even with insecticide applications. Upon detection of higher population of springtails in the field yet to be planted, soil moisture management could reduce the population pressure. For further infomation please contact me at svjoseph@ucdavis.edu or (831) 759-7359. You could also see a video of this subterranean springtails in the recent AgNETWest radio report.

It’s that time of year again when hot weather fuels the creation of ozone, or smog. Some pesticides emit volatile organic compounds (VOCs) that contribute to ozone formation. Using pesticides that release VOCs may be restricted in certain California locations between May 1 and October 31.

If you plan to apply a pesticide, use the Department of Pesticide Regulation’s VOC calculators to determine emissions from fumigant and nonfumigant pesticides. Get there by clicking on the Air Quality button at the top of each treatment table in the UC IPM Pest Management Guidelines for lettuce, spinach, or cole crops.

Simple steps can minimize the release of VOCs into the air: 

• Use pesticides only when necessary. 
• Decrease the amount of pesticide applied if appropriate. 
• Choose low-emission management methods.
• Avoid emulsifiable concentrate (EC) formulations and fumigants.

Ozone, or smog, is caused by mixing VOCs, nitrogen oxide, and sunshine. High levels of ozone can harm people and crops. Regions in California that do not meet federal or state air quality standards for ozone, called nonattainment areas, may restrict the use of pesticides that release VOCs.

Smoggy air in the San Joaquin Valley. Photo by David Rosen