- Author: Rachael Freeman Long
- Author: Amber Vinchesi-Vahl
A question came up about managing root-knot nematodes in processing tomato and lima bean rotations. Root-knot nematodes are tiny worm-like soil dwelling pests that cause root galling on plant roots, resulting in significant yield and quality losses. Symptoms of severe root-knot infestations include patches of chlorotic, stunted, necrotic, or wilted plants. These nematodes also predispose plants to other soilborne pathogens that cause root rot and wilt diseases. For example, a bean variety resistant to infection by the Fusarium wilt pathogen will become susceptible to this disease if infected with root-knot nematodes.
What is the link between nematodes in tomatoes and limas? Dr. Phil Roberts, Nematologist at UC Riverside shared the following response:
There are several root-knot nematode species and they differ in their response to resistance in tomato and various bean crops. Most common in our Sacramento Valley area are Meloidogyne incognita and M. javanica. These nematodes are normally controlled by Mi-1 gene based resistant tomatoes, but there are resistance-breaking populations so that could be the reason for the infection on tomato (unless the tomatoes grown were not actually resistant). A further possibility is that the species is M. hapla, which is not controlled by the tomato resistance. M. hapla tends to induce smaller pearl-like galls on tomato roots and is not common in the Sacramento and northern San Joaquin Valleys.
As to rotating with lima beans, limas are susceptible to these root-knot species but there are resistant varieties available. Beja Flor baby lima has strong root-knot resistance. It was bred to contain three resistance genes that do a good job of blocking M. incognita and M. javanica. It yields well with the caveat that Steve Temple (former UCCE legume specialist) used to remark that it is more Lygus bug susceptible than some varieties, so if a grower went with UC Beja Flor they would need to keep up on the Lygus management. UC Luna baby lima has no root knot resistance. Other lines carrying M. incognita (but not M. javanica) resistance are the large limas White Ventura N and UC92.
If root-knot nematodes are present in a field with a history of Fusarium wilt, choose varieties that are resistant to root-knot nematodes as well as to the particular Fusarium wilt race present when possible. Another option is to rotate with root-knot nematode resistant cowpeas (blackeyes) instead of limas. Based on host-range tests, some varieties of cowpea have more root-knot nematode resistance than tomato. For example, some root-knot nematode races are virulent and highly pathogenic to Mi-1 gene based resistant tomatoes but not to nematode resistant cowpeas.
We cut our blackeye bean (cowpea) research plots at UC Davis almost 3 weeks ago and they're still too green to harvest. If we tried now, the vines would get wrapped around the threshing cylinder. Several growers in the Sacramento Valley have mentioned that their corn has sat at the same moisture level for weeks and is not drying down either, as one would normally expect for this time of year. But, nothing is normal this year!
Why aren't our crops drying down?
Tragic fires throughout the West have pushed a lot of smoke and ash into the sky, creating fog-like conditions that reduce the intensity of the sun, shade crops, and lower temperatures. The blanket of smoke is like stepping into the shade under an awning on a 90oF day. This reduced sun intensity has affected the ability of crops to dry down in a timely manner. Increased humidity levels this past weeks haven't helped either.
While shading may be good for protecting tomatoes from sunburn with harvests running late due to COVID-related challenges, it is not good for drying down field crops.
With the smoke finally dissipating, drying conditions are improving. We ended up turning our blackeye bean crop over to increase aeration and help it dry down. Dry beans are sometimes turned to help dry the crop down, especially if they're rained on, but the challenge is to be careful to prevent shattering.
In corn, there aren't any easy solutions. One grower said their corn sat at 16.5% moisture for several weeks and finally they had to harvest it anyway. Dryers are available for drying corn and other crops to the proper storage moisture, but as we all know it's expensive and with low grain prices this affects the bottom line.
Last week, I visited a baby lima field in the southwest part of San Joaquin County that had overall poor pod set. Pods were filling lower in the canopy, but flowers had not set higher on the plants. The field, which was planted in late-June/early-July had an excellent stand, and ostensibly, good fertility and moisture status (Figure 1). There were two possible reasons for the poor pod set that immediately came to mind: 1) lygus damage and 2) heat stress.
I checked data from the CIMIS stations nearest to this field, which are the Brentwood and Manteca stations. Between May 1st and August 31st, the Brentwood station recorded 16 days with a temperature over 100°F, and the Manteca station recorded 9 days over 100°F. Most notably, the heatwave in mid-August struck at perfectly wrong timing. This field was about 50 days after planting, which is generally the prime time for bean flowering. The heatwave brought daytime temperatures over 105°F and nighttime temperatures that barely, if at all, dropped below 70°F. In fact, it is the high nighttime temperatures that will impair pod development by hindering pollen movement and rendering it sterile. This is not just the case for limas; it can happen with other dry beans, as shown by Rachael Long in this blog post from a couple weeks ago. Had the heatwave occurred earlier in the summer, it could have caused a split set, which is not desirable. The mid-August timing, however, means that day length is now too short for further pod development, and yield will likely be lower than expected.
Naturally, one should ask what would be considered a ‘high' nighttime temperature? Rachael remembers having a conversation roughly 20 years ago with UC dry bean breeder of that time, Steve Temple, who said that nighttime temperatures above 68°F will cause poor pod set. This is corroborated by recent work out of the University of Delaware that indicates nighttime temperatures of roughly 70°F impairing pod set. CIMIS recorded nighttime temperatures in that range. The grower indicated that some nights stayed closer to 80°F, which is the temperature at which breeders screen varieties for heat tolerance.
So, what can a grower do during a heatwave? Obviously, we can't control the weather, but it's important to ensure that beans are not moisture-stressed at bloom, and especially not when bloom occurs during a heatwave. Check the top 12 to 24 inches of the soil profile, and irrigate if the soil is dry. If in doubt about how much water is needed, check the reference evapotranspiration (ETo) and irrigate to replace at least 120 percent of your daily ETo. Daily August ETo in the San Joaquin Valley ranges from 0.2 to 0.3 inches per day, so growers would want to apply 120 percent of that amount. In the field that I visited, the crop looked very healthy and non-stressed, so there is no clear suggestion for a management practice that could have saved the set during our recent heatwave.
For more information on lima bean production in California, please see the UC production manual.
- Author: Rachael Freeman Long
Have you ever wondered about this damage to garbanzo beans where there's a hole clipped in the pod and the seed is missing (see photo)? In this case, the damage is from pesky ground squirrels that were foraging in and around our garbanzo research plots at UC Davis this spring. However, other culprits could include field mice or voles, rats, and pod borers such as corn earworm. If you suspect caterpillar worm pests, you should be able to find them easily enough in the plant canopy. Sometimes corn earworms move from corn fields into garbanzos, so watch for infestations from nearby corn fields. Field mammals are more elusive, though ground squirrels are active during the day and easy to spot.
Generally, garbanzos have few pests because the plants (including seed pods) are covered with tiny glands that secrete acids that help repel pests. These acids are strong enough to cause skin rashes and damage clothing. However, ground squirrels don't seem bothered at all by these plant acids as they thrived on our garbanzo seeds, green and dried alike! Looking back, we should have paid more attention to where the field trial was located, avoiding places where ground squirrels thrive, such as a nearby ditch bank. We also should have controlled them as soon as they were active.
Ground Squirrel Control. Various methods can be used to control ground squirrels around fields, including fumigation, trapping, and toxic baits. Of critical importance is the timing for control. Effective management depends heavily on understanding the unique life cycle and behavior of the California ground squirrel. Baiting with treated grain is effective in summer and fall because squirrels primarily feed on seeds during this period. Burrow fumigation is most effective in spring, when moist soil helps seal gasses in the burrow system. Fumigating at this time is also more effective in reducing ground squirrel numbers since squirrels die before they can reproduce. More information on ground squirrel management can be found on the UC IPM website for ground squirrel control at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7438.html.
- Author: Rachael Freeman Long
Recently, I received a call about a blackeye bean field in the San Joaquin Valley with a lot of bean pods that did not fill out at the tips (photo). I contacted the UC Riverside blackeye bean breeders Drs. Phil Roberts and Bao Lam Huynh and they shared that this problem is primarily caused by heat, which affects pollen viability and thus fertilization. Here's their response:
It [lack of pod fill] is the typical male-sterility symptom [lack of pollen viability] associated with extreme temperatures (heat or cold). Based on the planting date you gave, we just checked the temperature in Denair, CA [farm location] and noted that it was quite warm (~100) during the flowering time (40-50 days after planting) and recently during the pod filling stage, so heat must have been a main cause. The symptom could also be more severe if water is limiting.
Always be prepared with good irrigation management practices for all crops going into heatwaves, like the one we're having now. The minimum seasonal irrigation needed to produce a blackeye bean crop being managed for full yield from one pod set is 16 to 18 inches. This estimate includes a pre-irrigation of 4-inches, and irrigations of 4-inches when floral buds first appear, and 8 to 10 inches during 5 to 6 weeks of flowering and pod filling. If additional irrigations are needed during the vegetative stage, one could increase the total irrigation requirement to 20 or more inches. Irrigating for a second flush of pods could require an additional 8 to 12 inches of water. Irrigation requirements are further increased by any water required to leach salts or to compensate for an inefficient irrigation system.
Additional water may need to be applied during extreme heat events which drive plant transpiration rates to the limit. Make sure to check the soil moisture in the top 12 to 24 inches of the soil profile and apply additional water if the soil is dry. If in doubt about how much additional water is needed, check the reference evapotranspiration (ETo) and make sure to irrigate to replace at least 120% of your daily ETo in your area. The current (mid to late August) daily ETo in the San Joaquin Valley ranges from 0.25 to 0.30 in/day; make sure your applied irrigation replaces 120% of these values.
More information on growing blackeye beans can be found in the publication, UC ANR Blackeye bean production in California, http://beans.ucanr.edu/files/226601.pdf.