- Author: Richard Smith
Weed control in lettuce and other crops is a key issue this time of year. Purslane is particularly problematic and is adapted to warm conditions and can grow very rapidly especially during July and August. At times growers and PCA's are disappointed with the efficacy of Kerb on this weed. Kerb is effective in controlling purslane but it is readily leached and, if applied at planting, it can be moved below the zone of germinating weed seeds with the germination water. For instance, 6-8 hours of sprinkler water (1.5 to 2.0 inches) are commonly applied in the first germination water which can move the Kerb below the upper 0.5 inch of soil which is the zone where the weed seeds germinate; the movement of Kerb with the germination water is particularly problematic on sandy soils. Prefar does not leach and thus provides most of the purslane control when the two materials are tank mixed (Figure 1). However, Prefar does not control shepherd's purse or nightshades which can also be problematic in lettuce fields. Therefore, it would be advantageous to optimize the efficacy of Kerb to maximize the control of purslane as well as other weeds.
In the desert, the use of delayed applications of Kerb has been used for many years. Due to the large amounts of water that are applied in their hot conditions, Kerb is applied in the 2nd or 3rd germination water, approximately 3-5 days following the first germination water, just prior to the emergence of the lettuce seedlings. This technique can also be utilized in the Salinas Valley. We have looked at this technique over the years and have found it to improve the efficacy of Kerb (Figure 2). These data illustrate the loss of control of purslane by Kerb when applied before the 1st germination water, as well as the improvement in efficacy that results when applied following the 1st germination water. It also illustrates the role that Prefar plays in the control of purslane when the efficacy of Kerb is lost by leaching. It should be mentioned that the label states that the maximum amount of Kerb that can be applied through the sprinklers is 2.5 pints/A and the amount used in this trial was for experimental purposes only. Clearly there is benefit from applying the Kerb later in the 2nd or 3rd germination water, however, we observed that applying the Kerb at the end of the 1st germination water also provided improved efficacy of Kerb. Clearly, anything that helps to keep the Kerb in the top 0.5 inch of soil improves its efficacy.
Here are some details that need to be considered regarding the application of Kerb later in the germination phase of the crop: There is a need to use an injection pump and tank. We have typically used a tank with a circulating mechanism to keep the Kerb in suspension while the injection was occurring. The material needs to be injected into the mainline in a location where proper mixing can occur before it begins to flow down the laterals. The most difficult issue that growers face is the compatibility of the injection with surrounding crops. This is probably the greatest challenge and must be carefully thought through before attempting an application.
Another idea that we explored last year was the use of an additive to help retain the Kerb in the upper portion of the soil where it can be most active. However, we did not see improved efficacy in two 2018 trials (data not shown).
Many growers now are now using drip irrigation to germinate lettuce. Grower may apply the same amount of water with drip germination as with sprinklers, but the movement of the water is different which affects a surface applied material differently. With this method of germination, there are a couple of interesting dynamics that occur: 1) Kerb is not pushed too deep by this germination method and effectively reduces weed populations whether injected into the germ water (currently not a registered method of application) or sprayed on the soil surface and activated by the drip germination water (Table 1); and 2) fewer weeds emerge with drip germination than with sprinklers, regardless of the herbicide program.
Table 1. Effect of Kerb application (at 3 pints/A) method (surface applied, drip injected or untreated) and irrigation method (surface tape, buried tape or sprinkler) on weed densities, lettuce stand and visual injury.
- Author: Cheryl Reynolds
Summer is here, and we're halfway through 2019 already! Why not get jump on finishing up your continuing education units by taking online courses from the UC Statewide IPM Program (UC IPM). If you are a license or certificate holder from the California Department of Pesticide Regulation (DPR), and your last name begins with the letters M through Z, you should be receiving your renewal packet in August.
We're excited to announce some changes.
- In January, we switched all of our online courses to a new learning system located at https://campus.extension.org/. This new system has extensive technical support, is easier to navigate, and is more stable than the old one. Note that the extension platform offers courses from all across the country, including several providers from California. Look for the UC IPM logo to be sure you are taking one of our courses.
- We are pleased to announce that a brand-new online course on the Fuller rose beetle was added to our citrus integrated pest management IPM series. Dr. Beth Grafton-Cardwell, a citrus IPM specialist and research entomologist, and Dr. Joseph Morse, emeritus professor of entomology, developed the course. The course describes the life cycle, natural enemies, and management of Fuller rose beetle and explains why it is important for countries that export citrus. Fuller Rose Beetle has been approved by (DPR) for 1 hour of credit in the Other category and by Certified Crop Advisor (CCA) for 0.5 hour of IPM credit.
- Many of our courses are now credited not only by DPR for continuing education hours, but also by the California Structural Pest Control Board (SPCB), Certified Crop Advisor (CCA), Western Chapter of the International Society of Arboriculture (WCISA), and also by Arizona Department of Agriculture.
DPR encourages license and certificate holders to avoid the end-of-the-year rush and submit renewal applications by November 1 to ensure license renewal by January 1, 2020. Submitting your renewal early avoids late fees and gives you time to address any issues that may arise such as not having enough hours to successfully renew.
Another incentive to get a jump on completing your needed continuing education units (CEUs) with UC IPM's online courses is that we are offering an early-bird price for four of our most wanted courses until November 1st.
- Proper Pesticide Use to Avoid Illegal Residues (2 hours Laws and Regulations; early bird price $40, full price $80)
- Proper Selection, Use, and Removal of Personal Protective Equipment (1.5 hours Laws and Regulations; early bird price $30, full price $60)
- Pesticide Resistance (2 hours Other; early bird price $20, full price $40)
- Pesticide Application Equipment and Calibration (1.5 hours Other; early bird price $15, full price $30)
You can find all of our twenty-one courses listed on the UC IPM website at http://ipm.ucanr.edu/training/.
- Author: Alejandro Del Pozo-Valdivia
We are happy to announce that the diamondback moth capture data, presented as maps, is now housed in our own University of California Cooperative Extension Monterey website.
To access to these maps, simply click on the link below:
http://cemonterey.ucanr.edu/Agriculture/2019_Diamondback_moth_monitoring_maps/
These maps use the closest town or landmark where the traps are located to show moths per trap per day. Moth captures are presented as yellow bubbles. The bigger the bubble, the larger the population of moths is.
On the same page, you will also find the overall population fluctuations of these moths in the Valley, as a series chart.
We also stored the overall fluctuation of aphids and thrips numbers, captured in yellow sticky cards in our UCCE Monterey website. To access to these bar charts, click on the link below:
http://cemonterey.ucanr.edu/Agriculture/2019_Aphid_and_Thrips_Monitoring_Program/
If you would like to learn more about these three monitoring programs happening in the Salinas Valley, do not hesitate to contact Alejandro Del-Pozo at adelpozo@ucanr.edu or 831-759-7359.
- Author: Michael D Cahn
- Author: David Chambers
A tensiometer is a very useful tool for monitoring soil moisture status of vegetable and berry crops. Compared to other sensors that often require equipment such as dataloggers or a computer to collect readings, tensiometers can be easily read by irrigators in the field. Also, tensiometer readings are not affected by variations in soil texture, temperature, and salinity and they can operate without electricity (no batteries needed).
What is tension? Tensiometers measure soil moisture in units of negative pressure also known as tension. Tension is a measure of the force that plant roots need to exert to pull water from the soil pores. Large pores hold water with less force than small pores. As plants extract moisture from the soil, water is first taken up from the largest pores. As the soil dries roots need to exert more force to pull water from the smaller pores. Hence, high tension values mean that the soil is becoming dry.
How do tensiometers work? Tensiometers are filled with water (preferably distilled) that has been degassed by boiling. A key component of the tensiometer is a porous ceramic cup which allows water in the shaft of the tensiometer to freely pass into the soil without air bleeding though the small pores in the cup (Fig. 1). If the soil is not saturated, water will move from inside the cup into the unfilled soil pores. Because air cannot replace the space vacated by the exiting water, a vacuum develops in the shaft of the tensiometer that can be measured with an accurate gauge. Water will stop migrating from inside the tensiometer cup into the soil when the internal vacuum pressure of the tensiometer equals the soil tension, or the force needed to pull water from the soil pores. The vacuum gauge measures tension in units of kPa or cbars, which are equivalent (1 kPa = 1 cbar).
Interpretation of tension readings Because the tension value provides a sense of how much energy a plant would need to exert to suck water from the soil, tensiometer readings can be easily related to water stress in crops. At high tension values a plant experiences more water stress and growth slows. In addition, a tension reading has a similar meaning in terms of water stress whether the soil has a sandy, clay or loam texture.
Reliability of tensiometers The one Achilles' heal or weakness of the tensiometer is that if any air leaks into the instrument it will not retain a vacuum and the readings will be unreliable. There are several brands of commercial tensiometers available. Some are relatively inexpensive and simple to use, and others are more complex and can be interfaced with dataloggers to provide continuous readings throughout the day. Based on our experience, some of the most popular commercially available tensiometers often leak air and loses vacuum pressure, and in many cases the gauges do not provide accurate readings or are not durable. The loss of vacuum pressure means that the tensiometers need to be frequently refilled with degassed water. Also, irrigators may mistake a low reading to indicate that a crop has adequate moisture when in reality the soil may be dry.
A dependable tensiometer design We designed and tested a version of a tensiometer in 2018 that was simple to build and provided accurate readings for a material cost of less than $55 . The design improved the ability of the instrument to retain a vacuum at high tensions. Under moderately moist soil conditions the tensiometer usually required refilling with degassed water less than once per month. Even when the soil dried to tensions above the maximum range of the tensiometer (> 80 kPa), these tensiometers continued to hold a vacuum for about two weeks until all of the water in the shaft was depleted.
The following paragraphs describe the materials needed (Fig. 2) and procedures to build a tensiometer. The vendors of the materials are examples of ones that we use, but you may identify different or cheaper sources for these components. By carefully following these instructions, one should be able to build a dependable tensiometer that provides accurate tension readings.
Materials needed:
Ceramic cups
Vender: SoilMoisture Equipment Corporation, Santa Barbara CA (805-964-3525) Part Number 0655X01-B01M3, Dimensions: 0.875 inch OD x 2.75 inch length. Cost: $30.80 ea.
Epoxy (ceramic/plastic)
Vender: SoilMoisture Equipment Corporation, Santa Barbara CA (805-964-3525)
Part Number 0980V004, Description: 4 oz: epoxy and 4 oz hardener. Cost: $106 ea. Note that the epoxy/hardener is a sufficient volume to make several hundred tensiometers.
Vacuum gauge
Vender: Zoro.com/Grainger.com Part Number 4FMK3, Description: ¼ inch MNPT 2 inch diameter test vacuum gauge. Cost: $18.09 ea.
#1 size rubber stopper
Vender: Grainger.com Part Number 8DWU6, model RST1-S, Description: 24 mm neck, bottom diam. = 14 mm. Top diam. = 20 mm. Cost: $18.08 / 52 pieces
Schedule 40 PVC pipe (½ inch diameter) Vender: irrigation supply or hardware store
PVC “T”
Vender: irrigation supply or hardware store, Manufacturer: Spears Inc. Part number 402-072, Description: ½ inch slip x ¼ inch threaded reducing "T."
PVC glue (gray) and purple primer
Vender: irrigation supply or hardware store
Gas pipe thread sealant (white or blue paste type)
Vender: irrigation supply or hardware store
Painters masking tape
Vender: hardware store
Petroleum Jelly (Vasoline)
Vender: pharmacy
Tools needed:
- PVC saw or PVC cutting tool
- Aluminum Oxide grinding stone, Manufacturer: Forney Part Number: A11 60028 Description: 7/8 in [23 mm] diam. x 2 inch [50.8mm] length
- Power hand-held drill
- Miter box
- Pocket knife
Procedures
1. Cut PVC pipe sections in the following lengths
1 foot depth tensiometer: top shaft = 4 inches, bottom shaft = 17 inches
2 foot depth tensiometer: top shaft = 4inches, bottom shaft = 30 inches
It is advisable to cut the bottom shaft about 1-inch longer than indicated above and then carefully cut the lower end of the shaft using the miter box or electric miter saw to assure that it is cut at a 90-degree angle. The ceramic cup will fit crooked on the end of the shaft if the cut deviates from 90 degrees.
- First glue the top shaft and then the bottom shaft to the ½ PVC “T” using the PVC glue. Make sure that you do not glue the end of the bottom shaft that was trimmed to 90 degrees. In a well-ventilated location, apply PVC primer to both the end of the shaft and the inside of the “slip” end of the “T”. Then apply gray PVC glue to both sides, and push the parts together, and hold in place for about 30 seconds to 1 minute. Tip: slightly twist the parts by about 30 degrees immediately after gluing to assure that the parts are secure. Also cover the non-glued areas with painter's tape to prevent the outside from becoming covered with glue.
- Slightly bevel the inside of the lower end of the bottom shaft using the handheld drill and grinding stone (Fig. 3). Alternatively, one can use a knife to bevel the end. Whether using the drill or the knife to bevel the inside of the pipe, stop periodically and test fit the ceramic cup. This way you will not remove too much material, and will quickly get a feel for the appropriate amount to remove.
Figure 3. A drill is used to bevel the lower end of the tensiometer shaft to accommodate the ceramic cup. - Use epoxy to glue the ceramic cup to the lower end of the bottom shaft. Protect the ceramic cup during the gluing process by covering the outside with painter's tape (Fig. 4). Check that the ceramic cup fits snuggly into the PVC tube and is aligned straight. If using the epoxy from SoilMoisture equipment epoxy, mix up 1-part epoxy with 1-part hardener. Mix thoroughly. Only a small amount of epoxy is needed to coat the throat of the ceramic cup and the inside of the PVC tube, so it may be best to glue several tensiometers at the same time so that the epoxy is not wasted. One can usually glue no more than 20 to 40 cups at a time becaue the epoxy begins to cure after an hour. Approximately 20 ml of epoxy is needed for 20 tensiometers. The cure time is temperature dependent. Full cure is 8 hours at 77 °F. It is best to allow more time for curing. After gluing, painter's tape can be used to secure the cup to the shaft. Take care when securing the two with the tape to assure that the cup is aligned with the PVC shaft. Let the glue set for at least 24 hours with the tensiometer supported with the cup-end up in a vertical position. Tip: best if parts are glued at temperatures above 65 °F. More hardener may be needed at lower temperatures. Also, it is advisable to first test a small batch of epoxy to assure that the proportion of hardener to epoxy is enough for epoxy to set up hard.
Figure 4. Use painter’s tape to prevent glue from coating the PVC shaft and ceramic cup. - Coat the ¼ inch male threads of the gauge with pipe thread sealant and hand screw on the vacuum gauge. Tip: do not over tighten or the PVC “T” will crack!
- Fill the tensiometer fully with degassed distilled water. The water can be degassed by boiling it and allowing it to cool.
- Coat the lower end of the rubber stopper with a thin film of petroleum jelly and insert into the top end of the tensiometer with a light twist to firmly seat the stopper (A loose stopper is the main cause for vacuum leaks).
Figure 5. Finished tensiometer is ready for testing.
Testing the tensiometer for air (vacuum) leaks:
After filling the tensiometer with water and sealing it with a rubber stopper, wrap a dry paper towel on the end of the ceramic cup and hold it tightly (Fig. 6). If the tensiometer is filled with degassed water, the tension should quickly increase to about 20 to 30 kPa as the towel absorbs water from the cup. If the gauge does not increase above 0, air is likely leaking into the tensiometer. Check the glue joints and assure that the stopper is tightly in place.
If the tension quickly increases to more than 20 kPa, then leave the tensiometer out in the sun to assure that the tension rises to above 70 to 80 kPa. This may take some time, minutes to hours, depending on the ambient temperature. If the tension does not increase to a high value, then check glue joints and the stopper. Also check that the gauge is securely threaded into the PVC “T.”
Installing tensiometers in the field:
Proper installation of a tensiometer in the field will achieve close contact between the ceramic cup and surrounding soil. Using a soil probe with a ½ inch diameter shaft, make a pilot hole to a depth a few inches shallower that the depth of installation (Fig. 7). Make a soil water slurry by thoroughly mixing soil with the water to a pancake batter-like consistency. Add some slurry into the hole and push the tensiometer to the desired depth (Fig. 8). The soil slurry assures that water can freely move between the ceramic cup and the surrounding soil and fills the voids between the hole and tensiometer shaft. Formation of air gaps between the ceramic cup and the soil will lessen the accuracy of tensiometer readings. After two days of equilibration, the tensiometer reading should accurately reflect the tension of the soil.
- Author: Alejandro Del Pozo-Valdivia
We continue the effort of monitoring diamondback moth (DBM) across the Salinas Valley using sex pheromone baited traps, as shown in the picture above. We have been adding additional traps to cover a larger area along Highway 101. We have daily moth capture data from Castroville to Greenfield. The chart below summarizes these daily captures from our pheromone traps.
As stated in a previous blog post, higher numbers of DBM have been usually recorded in Castroville. It seems like we just passed a generation of adults during late March to early April. Currently, DBM capture numbers are going down. Lower adults in the system could be paired with more caterpillars feeding on several host plants.
We have set up yellow sticky cards to track the overall population of winged aphids and thrips. These sticky cards are in the same locations as the pheromone traps. At this point, data for aphids and thrips is not broken down at the species level.
From the chart above, there was a flight of aphids during late March to early April. Some PCAs mentioned to me that foxglove aphid started to show up in their fields during that time period. It seems now that winged aphid numbers are going down. However, it does not mean that numbers of aphids in our crops are decreasing. We might be facing higher population of wingless aphids in our crops right now.
We need to keep an eye on population dynamics of thrips in the Valley. The ultimate goal is to be better prepared this season to manage those creatures and reduce the incidence of INSV virus. The chart below shows captures of thrips in our sticky cards.
It seems like thrips populations had a spike two weeks ago. Currently, thrips numbers are going down. I believe that keeping track of the fluctuation of thrips numbers in our Valley would help us detect large populations of this pest. There is a need to alert PCAs when the front of a 'thrips wave' would happen.
If you are interested in getting more information on this monitoring effort, please do not hesitate in contacting Alejandro Del-Pozo at 831-759-7359 or adelpozo@ucanr.edu.
