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 firstname.lastname@example.org or (831) 759-7359. You could also see a video of this subterranean springtails in the recent AgNETWest radio report.
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.
- Author: Richard Smith
Cilantro was produced on 5,543 acres in Monterey and Ventura Counties in 2011. The production of cilantro has shifted to high density 80-inch wide beds and a large proportion is now mechanically harvested. Hand weeding high density beds is very expensive and reduces the economic viability of this crop. As a result, there is a need for excellent weed control. Two broadleaf herbicides were registered on cilantro: Prefar and Caparol. Prefar was registered for a number of years and provides good control of a number of key weeds in cilantro such as purslane, lambsquarter and pigweed. Caparol was registered in 2012 and provides good weed control of a wider spectrum of weeds including the nightshades, shepherd’s purse, sow thistle, groundsel and others (see tables below).
Here is the situation with Prefar: EPA moved cilantro (also Mexican & Chinese parsley) out of the "Leafy vegetables" crop group 4 and placed it in the "Herbs and Spices" crop group 19. The issue is that crop group 19 Herbs and Spices has no tolerance for Prefar. Without a tolerance, Gowan Corp. can no longer support the 24c for cilantro. It places growers in a tricky situation, because they may have Prefar with the old label in reserve, but any detectable levels of Prefar residues are detected on cilantro, it could result in seizure of the crop. This is a regulatory snafu that may take some time to untangle; work is being done to resolve this situation but it is unclear how long it will take to resolve.
Caparol is also registered for use on cilantro, but there is a plant back restriction of 12 months prior to planting lettuce, broccoli, cauliflower and spinach. This is of course very difficult to work with this restriction in the Salinas and other coastal valleys.
Other weed control options: bed fumigation of cilantro prior to planting can be highly effective, but issues with the cost and working around buffer zones makes this option difficult to fit into a grower’s production budget as well as schedule. Cultural practices such as pregermination followed by shallow cultivation of emerged weeds prior to planting can help reduce weed pressure. Cilantro seed germinates slowly which opens the possibility of burning off a flush of weeds (with an herbicide or propane flamer) following planting but prior to the emergence of the cilantro. This is a tricky, but highly effective technique for reducing weed density.
In summary, we have a number of regulatory issues that need to be addressed in order use the broadleaf herbicides without difficulty. We will need to continue to work with the regulators and registrants to resolve these issues as quick as possible.
(Click on tables and images to Enlarge)
- Author: Steven T. Koike
Coastal California growers, pest control advisors, and other field professionals might be on the alert for early outbreaks of lettuce problems caused by viruses. In particular, early confirmations have been made of the Tomato Spotted Wilt Virus (TSWV) on lettuce in this region. Affected leaves have tan, brown, or blackish spots and dead areas; this necrotic tissue can resemble damage caused by pesticide or fertilizer applications (see photos below). Some leaf yellowing can also be observed. If disease is advanced, symptoms can also be found on the newer leaves near the center of the plant axis. If plants are affected early in their development, growth can be stunted. Symptoms caused by TSWV in lettuce are indistinguishable from symptoms caused by the closely related Impatiens necrotic stunt virus (INSV) which in some seasons can be commonly found on lettuce in the Salinas Valley. All lettuce types (iceberg, romaine, greenleaf, redleaf, butter) are susceptible to both TSWV and INSV. Both viruses are spread by thrips, are found in hundreds of crop and weed species, and are not seedborne. In our coastal region, TSWV and INSV are spread only by the western flower thrips (Frankliniella occidentalis).
Our laboratory has confirmed TSWV on lettuce in late March, which is rather early for such developments. PCAs also report early buildups of thrips populations in lettuce and other fields. The relatively dry spring is resulting in early drying up and senescing of weeds and hillside vegetation; this early decline of surrounding vegetation very likely is driving thrips populations into fields earlier than normal. Lettuce growers should be aware of possible early problems due to thrips vectoring tospoviruses into their fields.
Lettuce with tospovirus-like symptoms can be sent for analysis to the UC Cooperative Extension diagnostic laboratory in Salinas.
Tomato spotted wilt on lettuce.
Impatiens necrotic spot on lettuce
Impatiens necrotic spot on lettuce