- Author: Richard Smith
Leeks were grown on 589 acres in Monterey County in 2018 and were worth $10.8 million. Depending on the planting date, they can be in the field for 120 or more days, particularly if they are over wintered. They can be grown from seed, but are commonly transplanted to overcome slow initial plant growth. Weed control in leeks is quite challenging because, like onions, they never form a dense crop canopy that can effectively compete with weeds. In addition, given the long crop cycle, a leek planting may experience flushes of both cool and warm season weeds.
Weed control options in organic leeks consist of 1) locating leek planting on blocks with low weed pressure (e.g. blocks with careful weed control in prior crop rotations), 2) utilizing transplants (to get a head start on weeds), 3) use of preirrigation to germinate a flush of weeds followed by shallow cultivation or flaming to kill them, 4) close cultivation of weeds during the production cycle and 5) hand removal of weeds that escape these aforementioned control methods. Weed control in organic leeks can be effective, but in general, weeding costs can be quite high given the long crop cycle and the need for multiple hand weedings.
In conventional leek production, all the practices just mentioned for use in organic production are also used. In addition, preemergent and post emergent herbicides are available that provide further weed control:
This array of materials provides tools to burn off a flush of weeds prior to planting or transplanting, preemergent control of weeds and post emergent control of grass weeds. What is missing is a post emergent herbicide that controls broadleaf weeds.
Over the past three years we have evaluated Caparol and Lorox as potential post emergent treatments for leeks. Caparol is registered for use on leeks in Canada and the IR4 Program is developing a tolerance for this material in the US. We are working with the IR4 program to conduct crop safety evaluations to provide data to support its eventual registration.
In a 2018 trial Caparol and Lorox at all rates provided excellent weed control on both evaluation dates (Table 1, and Photo 1.). Caparol and Lorox were both safe on leeks but caused a curious bending of older leaves early in the production cycle (Photo 2); the plants eventually grew out of this symptom and it did not appear to affect the yield. The bent leaves are trimmed off and it does not appear to be a quality issue for the marketability of mature leeks. In the 2019 trial rates above 0.5 lb a.i./A of Lorox reduced leek yield (data not shown). Lorox has the advantage of controlling yellow nutsedge. We observed that Lorox at 1.0 lb a.i./A provided selective control of yellow nutsedge (Photo 3).
In 2019 we tested the use of Caparol and a liquid formulation of linuron, Linex 4L, for safety and efficacy on onions. We applied these materials at the 2nd, 3rd and 4th true leaf stage. Both materials were safe on onions, but there was greater safety when applied at the later growth stages. For more information on these trials go to: http://cemonterey.ucanr.edu/Vegetable_Crops/Weed_Reports/.
- Author: Alejandro Del Pozo-Valdivia
- Author: Alejandro Del Pozo-Valdivia
On Wednesday October 9th, a Brussels sprout plant sample was submitted to our Entomology laboratory for insect identification.
At the naked eye, we observed some webbing and specks on the leaf (See Fig. 1).
Fig. 1. Leaf of Brussels sprout showing some webbing and 'specks'. Affected areas are highlighted with the yellow circles.
Under magnification, we were able to see eggs, nymphs and adults of the two spotted spider mite (TSSM), Tetranychus urticae (See Fig. 2). Adults of these specimens have the two black spots on the lateral sides of the anterior end of the podosoma, the area located below their mouth parts.
Fig. 2. Eggs, nymphs and adults of two spotted spider mites on the leaf of Brussels sprout.
TSSM is one of the most polyphagous mites, having several host plants around the world. Females disperse by putting silk strands right after mating and before producing eggs. Dispersing females climb to the top of the plant and specimens are carried out by the wind. This phenomenon called ballooning, aids mites to float through the air and disperse longer distances to reach favorable host plants.
It is highly advised that Brussels sprout growers and PCAs walking this crop, pay close attention to leaves within the canopy to potentially identify the presence of TSSW in this crop.
If you believe you may have TSSM in your Brussels sprouts, please send us a plant sample at 1432 Abbott St. in Salinas for confirming identification (free service), or call us at 831-759-7359 to obtain additional information on this pest.
- Author: Lennis Arriaga
- Author: Richard Smith
- Author: Michael Cahn
During the past two years acreage of season-long drip in lettuce has increased rapidly in the Salinas and adjacent valleys. Using drip for the entire crop cycle allows growers to germinate seeded crops with buried tape (Photo 1), and eliminates labor needed for installing and removing sprinklers. The rapid expansion of this irrigation practice is due to 1) reliable thin-walled single-use drip tape which assures high application uniformity for less cost than thick walled tape; 2) Better injection equipment that can uniformly place drip tape 2-3 inches below the soil surface allowing cultivation without damaging the tape (Photo 2), and 3) development of tape removal equipment that saves labor and efficiently bundles the tape for recycling (Photo 3). The use of drip for germinating lettuce often can improve the uniformity of stands and save water by eliminating common problems associated with using sprinklers such as emergence patterns caused by wind and crusting of the soil surface. Drip germination works best on light to medium textured soil types such as sandy loams, gravelly sandy loams, loams, and silt loams (e.g. along the river and on the eastside of the Salinas Valley).
Unlike sprinklers which infiltrate water at the soil surface, water applied by buried drip wicks upward keeping herbicides and fertilizers sprayed on the bed tops close to the soil surface. The upward movement of moisture from buried drip tape and subsequent evaporation of water from the bed top yields a net accumulation of salts (including nitrate) near the soil surface (Photo 4). This upward movement of applied materials benefits the preemergent herbicide, Kerb, which is often pushed too deep in the soil by sprinkler applied water at germination. The amount of wetting of the soil surface provided by drip germination is sufficient to set Kerb and keep it in the zone where weed seeds germinate which improves its effectiveness (for more information on this subject go to: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30847).
With buried drip, surface-applied fertilizers used as anticrustants or for thinning by automated thinners are not moved deep enough into the soil to be taken up by the lettuce crop during the early season. In one evaluation, we observed that the fertilizers were strongly stratified in the top inch of soil. Soil samples of the top six inches of soil by one-inch increments indicate that the nitrate levels in the top inch of soil are commonly higher than the deeper in the profile due to the upward movement of salts by evaporation mentioned above (Table 1). However, following the application of 20 gallons of 28-0-0-5 for thinning, the levels of mineral nitrogen (ammonium-N and nitrate-N) became extremely high (> 200 ppm NO3-N) and did not decline for the two weeks of the evaluation. In another field evaluation in which nitrogen fertilizer was applied to the soil surface (as an anticrustant (5-20-0) and for thinning (14-0-0-5)) the nitrogen remained in the upper two inches of soil for more than 5 weeks. This nitrogen just below the surface would be unavailable for crop growth because the soil is dry and root growth is minimal.
Table 1. Total mineral nitrogen (ammonium-N + nitrate-N) in the top 6 inches of soil. May 22 – prior to thinning; three subsequent sampling dates following application of 28-0-0-5 fertilizer by an autothinner
Since growers must report the total nitrogen applied to vegetables to the Regional Water Quality Control Board (RWQCB), the nitrogen remaining on the soil surface creates a problem. For instance, a typical application of 20 gallons of 14-0-0-5 contains 29 lbs of nitrogen/acre. This nitrogen is reported to the RWQCB but does not necessarily provide nitrogen for crop growth. More nitrogen would need to be added to keep up with the N demand of the crop. It would be advantageous to use materials in the autothinners that contain no or low amounts of nitrogen.
High levels of nitrogen on the surface also creates a challenge for collecting an accurate soil sample for determining plant-available nitrogen using the nitrate quick test or laboratory analysis. Photo 5 shows the results of three measurements: 1) high levels of nitrate-nitrogen found in the top 2 inches of soil (test strip on the left); 2) moderate amount of nitrate-nitrogen found in the 2 to12 inch layer (top 2 inches scraped off, test strip in the middle); and 3) high levels of nitrate-nitrogen found in the top 12 inches of soil (top 2-inches of soil is not scraped away, test strip on the right). We have always recommended scraping the dry surface soil away before collecting a soil core (see https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4406), however, the extremely high amounts of nitrate-nitrogen in the top 2 inches of drip irrigated fields that are autothinned with a nitrogen fertilizer makes this practices particularly critical in order to not over estimate the amount of plant-available nitrogen in the soil when making critical fertilizer application decisions.
- Season-long use of buried drip keeps herbicides and soil applied fertilizers (from anti-crustants and automated thinners) close to the surface due to the water wicking upward.
- Surface applied fertilizers remain in the top 2 inches of soil and are not plant available for much of the season. Ideally, a zero or low nitrogen containing thinning chemical would avoid this issue.
- It is important to scrape away the top two inches of soil when collecting samples for nitrate testing in order to not over estimate the amount of plant-available nitrogen when making fertilizer application decisions.