Just when you thought we knew all the devastating pests of avocado, along comes another one, this showing up in the Piru area of Ventura County - bagrada bug. The infestation is in huge numbers covering the stems and leaves of the tree, leaving fecal droppings on the backsides of leaves. The insects have caused some defoliation and damage to terminals. They lay their eggs in crevices in the soil and sometimes on the plant. Maybe mulching would help in their control. The orchard will be sprayed soon to control them.
The bagrada bug, Bagrada hilaris, also called the painted bug, is a stink bug that attacks various vegetable crops, weedy mustards and several vegetable crops like cabbage, broccoli and cauliflower. It is particularly devastating to young seedlings and leafy mustard greens.
Bagrada bugs often infest wild mustard weeds, which are pervasive in California on hillsides and in agricultural corridors in late winter to early spring. Populations rapidly increase in the weeds when seasonal temperatures rise. Record numbers of bugs can invade newly planted cole crops after mustard weeds dry out in late summer.
The bagrada bug is an invasive pest species, native to Africa, which has spread to India, Pakistan, parts of Southeast Asia, and Italy. In the United States, it was first found in Los Angeles County in 2008. By 2011, the pest had disseminated throughout Southern California to include San Diego, Imperial, Orange, Riverside, San Bernardino, and Ventura counties. In September 2012, the pest moved northward to Santa Barbara and San Luis Obispo counties and recently (2013) the Bagrada bug was found in Fresno, Tulare, and Monterey counties.
In this case, it appears that with the drought all the mustard on the hillsides has dried up and the only food is the young avocados on the hillside. Interestingly, the neighboring canyon is infested with harlequin bug (Murgantia histronica) another stink bug with similar coloration but about three times larger than the bagrada bug. Once rains return, these pests should retreat back to the wild hillsides.
Images: 1) Dry hillside where infestation is occurring. 2) Defoliation caused by bug. 3) Fecal pellets on underside of leaves. 4) Bagrada adults and nymphs.
This is a story about phone calls that come in to my message machine. Yesterday I got 3 calls from PCAs (Pest Control Advisors) and two from growers. The two from growers were from a Papaya grower and the other from a dragon fruit grower that I am working with to develop an industry here in Santa Barbara/Ventura. One is in Carp the other in Montecito. The PCA calls were from two that work on avocado and the other from a citrus grower. I either get a call from an avocado grower direct because they can't afford a PCA or from the manager or the PCA of larger farms. From citrus it is usually the manager or the PCA. These are more developed industries and the grower usually lets the workers take care of problems because they are so familiar with the operations. When it ‘s a new crop, the owner steps in. They want to know all that can go wrong with this new crop.
Blueberries are expanding now along the coast and when we first started working on them 15 years ago, our collaborators were in touch with us constantly. Now it's the managers who call. Its now a developed industry. The same for coffee. When we started working on it we worked closely with out cooperators, now there is a coffee cooperative that takes care of itself. We work with new things. One of the calls from an avocado PCA was about a farm that is being infested with bagrada bug. Everything in the area has dried up from the drought. The bagarada bug normally goes after plants in the brassica family (cabbage, mustard, etc.), many of which are native and growing along streams and on hillsides. The streams and hills have dried up and the bug is now going to the new avocado leaf tissue and the PCA wanted the bug identified and to provide a solution to the problem.
Sometimes the weather works for us and sometimes against us. We've got a parasitic wasp for controlling olive fruit fly. We went out all over southern Santa Barabara county to groves of olive trees to determine where to release the wasp and could find healthy olives, but no olive fruit. No where to make to make releases this year. The weather plays tricks on us. But we keep looking for solutions. Maybe next year we will be able to study if and how the wasp controls olive fruit fly. It does in France.
With the drought our perpetual salt problems are exacerbated due to less water and often more saline water. The question keeps coming up if gypsum (calcium sulfate) can help correct the problem. And the answer is maybe, but along the coast, probably not. The problem there is confusion about what is a saline soil and what is a sodic soil. A saline soil is one that is dominated by salts, but has a pH below 8.5 and can have a white crust that will actually taste salty. A sodic soil is one dominated by sodium, has a pH above 8.5 and can be saline, as well. Often though, there is a brownish cast to the surface salt crust. This is caused by dispersion (dissolved) of soil organic matter caused by the high pH. It's like cooking with vinegar when you make ceviche out of fish. Saline soils often have a high calcium content and may have sodium, but at a very low ratio compared to calcium. Most of the sodic soils in California are found in the Central and Imperial Valleys. Along the coast, the soils, if they have a problem, are largely saline.
The way gypsum works, is that the added calcium displaces soil sodium, pushing it lower in the soil column. The process also requires a lot of water to move the sodium through the soil column.
So the answer is, along the coast, gypsum is unlikely to improve soil conditions. However, there are other instances where it might help. In the San Luis Obispo area there are lots of serpentine derived soils that have a high magnesium content relative to calcium. And they commonly aren't saline, just an imbalance between the two cations. This can lead to infiltration problems and calcium deficiency in plants. Apples are especially sensitive to this high Mg:Ca ratio and develop a condition called “bitter pit”, a surface, brown pitting in the skin. There are other crops, like celery that are especially sensitive, but even avocado can be mildly affected. In the case of magnesium imbalance, gypsum can help.
I just raked up all the leaves under the avocado and it looks so nice. PUT THEM RIGHT BACK. The avocado is shallow-rooted and really depends on the natural leaf mulch to protect its roots. In fact the roots will actually colonize the rotted leaves as if it were soil. This mulch is also a first line of defense against root rot. The decomposing leaves create a hostile environment to the microorganism that causes the disease. The mulch also helps to reduce evaporative loss of water and therefore reduces water needs. Avocado growers will actually spread mulch in cases where trees are too young to produce adequate leaf drop for mulch or in windy areas where mulch has blown away. The key to remember is that the mulch should be kept at least six inches away from the trunk to avoid collar rot which can be causes by keeping a moist mulch against the trunk.
Mature avocados may be a big tree, but they have very shallow roots. The bulk of them are in the top 8 inches of soil. The tree therefore does not have access to a large volume of stored water. As opposed to a deep rooted walnut, they need frequent, small amounts of water. A young tree in the summer might need multiple applications per week, but because the root system is small, each application may only be 5-20 gallons. An older tree with its wider rooting pattern may go a week to a month between irrigations depending on the weather and rainfall. Proper irrigation is the best way to keep the avocado from getting root rot. Both over and under irrigation can induce the conditions for root rot, although over irrigation is more common. And remember, it is not just the amount applied at an irrigation, but the timing that is important, as well. Because you are managing such a shallow root system, just poking your finger into the root system will tell you if there is adequate moisture there before you irrigate again.