- Author: Jeanette Warnert
This article is reproduced because stinkbugs can attack avocado stems and weaken them, causing fruit drop. It' not clear that this species of stinkbug will attack avocado, but there is a possibility and we should all be on the lookout for it. Now we are caught between the two reproducing populations of Los Angeles and Sacramento Counties.
A well-established and reproducing population of brown marmorated stink bugs (BSMB) has been found in a Midtown Sacramento neighborhood, reported Chuck Ingels, UC Cooperative Extension advisor for Sacramento County. The infestation seems to be centered around 13th St., south of Capital Park. This is the first reproducing population in California outside Los Angeles County.
Ingels said he had no difficulty finding the pests on tree foliage and flying around when he visited the site last week. The California Department of Agriculture has designated BMSB a Class B pest.
"This is the worst invasive pest we've ever had in California, but there is no funding to attempt to eradicate it, nor is there a mandate to do so," Ingels said.
Brown marmorated stink bug affects many different crops and is a serious residential problem. It moves around easily, so can be expected to spread. It can fly up to a half mile at a time and also travels long distances by hitching rides in vehicles or inside furniture or other articles when they are moved, often during winter months. As a result, most new infestations are found in urban areas.
Brown marmorated stink bugs are native to China, Japan and Korea. They were first documented in the in the United States in Pennsylvania in 2001, but was likely established there several years earlier. The pest has spread throughout Pennsylvania, is believed to be established in at least 15 states, and has been found occasionally in more than a dozen additional states. In 2004, BMSB made its way to Oregon and is now established in northwest Oregon and a portion of Southern Washington. The National Agricultural Pest Information System maintains a map showing current infestations, but it does not yet show California finds. The pest has been present in Los Angeles County for 6 years.
BMSB feeds on dozens of California crops, including apples, pears, cherries, peaches, melons, corn, tomatoes, berries and grapes. Feeding on fruit creates pock marks and distortions that make the fruit unmarketable. In grapes, berries collapse and rot increases. Wine tasters have been able to detect stink bug odor in wines made from grapes that had 10 bugs in a 35-pound lug. It is also a pest of many ornamentals, especially fruit-bearing trees, princess tree (Paulownia tomentosa), common Catalpa (Catalpa bignonioides) and tree-of–heaven (Ailanthus altissima).
In addition to the damage caused by the BMSB feeding, the "true bug" can cause disturbing problems for homeowners in the winter. When the weather cools down, bugs migrate in droves to sheltered areas, including inside homes and buildings.
"These bugs aggregate in such numbers that there are reports of people using manure shovels and five-gallon buckets to dispose of them," Ingels said. "The strong, unpleasant odor the insects emit when disturbed makes cleanup still more daunting.
BSMB is a pest in its homeland, but is mostly controlled by parasitic wasps. USDA researchers have collected parasitic wasps in Asia, but they must be tested extensively before they can be released in California, a process that will take until 2016.
"Parasitism is our best hope for reducing populations," Ingels said. "Chemical control of BMSB is very challenging."
Ingels said the best way to keep them out of homes is to exclude them by sealing off any potential entry points, especially around window air conditioning units. Insecticides that have been shown to be effective in the lab are often less effective in the field. In and around the home, insecticides that have efficacy are mostly pyrethroids and neonicotinoids, both of which can have harmful off-site effects.
Pesticides showing efficacy on farms also include organophosphates and carbamates. But growers have worked hard to develop effective Integrated Pest Management programs, and the use of these broad spectrum sprays will set these programs back. There are also pest resistance concerns with increasing use of these products.
Control for organic growers and home gardeners will be most troublesome, and involves the use of row covers, trap crops, pheromone traps, and predator insects. Ingels is asking growers to be on the lookout for BMSB.
"Because they are strong fliers, it's just a matter of time before they reach farms," Ingels said.
The pest can be distinguished from ordinary brown stink bugs by its larger size, marble-like coloring on its shield and white markings on the extended edge of the abdomen. BSMB also has distinctive white bands on the antennae and legs. The UC Integrated Pest Management Program has posted a video on YouTube to aid in identifying the pest.
Traps with sex pheromones or other attractants can be used to monitor for the pest, but they are often poor at trapping the bugs even when populations are high. The best monitoring method is to inspect foliage throughout the year, and larger branches in late summer and fall for aggregating bugs. A quick method is to beat foliage over a piece of cardboard or sheet. If suspected BSMB are found, place some in a container and note where and when they were collected. Take the sealed container to the county agricultural commissioner or local UC Cooperative Extension office.
- Author: Gary Bender
Since our last article on high-density avocados appeared in Topics in Subtropics (Vol. 10 no. 1, Spring 2012) we have had a lot of questions from growers concerning the cost of installation of such a grove. We have also had a lot of interest from potential winegrape growers who think this might be the way to go given that wine-grapes use about 25% of the amount of water per acre compared to avocados. For higher quality wines growers use less water, but harvest lower pounds/acre.
I am currently advising a student at Cal State San Marcos who is doing a cost study for removing an avocado grove and installing a winegrape planting in San Diego County. Hopefully we will have an article on that in the near future.
We don’t have a lot of experience in high density avocados but we will try to show some costs to help you decide.
Clearing an older grove can get expensive. In a study we did in 2010 we found that it cost $40/tree to cut a tree down, haul the cut wood down to a firewood stack and haul to small branches to a chipper. The old stump is usually killed with a herbicide and left in place to rot. So, just to remove a tree at 109 trees/acre may cost $4,360 per acre.
For our high density planting we will be planting Hass avocados grafted on Dusa rootstock. We are using this rootstock because it appears from several trials to be a good rootstock for resistance to avocado root rot in the well-draining hillside soils in San Diego County.
The current price is about $30/tree (plus or minus). For a 10’ x 10’ spacing we would plant about 435 trees per acre, this would be an initial cost of $13,500/acre. We are not calculating the cost of a grove road installation, and we are assuming that the entire acre would be planted.
Planting cost: digging, planting, wrapping and staking trees takes about 15 minutes per tree. This includes carrying the tree to the hole. At 435 trees per acre, this would take about 109 hrs. At $14/hr, this would cost $1526/ac. Stakes (435) at $2.25/stake would cost $979/ac.
The irrigation system installation would cost $2,660/ac. This is based on an entire system being installed in a 20 acre block, divided by 20 to get the cost per acre.
There are quite a few other costs that you can see from our complete avocado cost study, but these basic costs will get the trees in the ground (Table 1).
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Table 1. Basic costs per acre for the installation of a high density avocado grove. It is assumed that land is cleared and ready to plant. Installations of grove roads are not considered. |
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Trees (Hass on Dusa rootstock) |
$13,500 |
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Planting (digging, planting and wrapping) |
$1,526 |
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Stakes |
$979 |
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Irrigation system |
$2,660 |
|
Total per acre |
$18,665 |
If you are thinking about planting 10 acres, then you would need $186,650 in the bank to get the trees in the ground. There will be some shifting of costs because this study does not include clearing or building of grove roads, and with grove roads you will be planting less numbers of trees/acre.
Will you make more money in the long run? That is the question we are trying to answer with our high density trial in Valley Center.
Reference
Bender, G.S. and E. Takele. 2010. A guide to estimate compensation for loss of a single avocado tree. University of California Cooperative Extension county publication AV 606.
Takele, E., Bender, G.S., and M.Vue. 2011. Avocado sample establishment and production costs and profitability analysis for San Diego and Riverside counties, conventional production practices. http://coststudies.ucdavis.edu/
- Author: Ben Faber
It’s that time of year when citrus and avocado growers need to collect leaf samples for nutrient analysis to guide fertilizer applications. Leaves are collected between August 15 and October 15 and sent to the lab for analysis. For perennial crops, leaf analysis is the most important guideline for managing tree nutrient applications. Many growers think that soil analysis is as important as leaf analysis, and is for annual crops, but is much less valuable for tree crops. Because a tree stores nutrients in its various parts, such as roots, trunk, branches, stems and leaves, it does not have to get all of its immediate nutrients from the soil the way a lettuce plant does. Trees also have a root association with beneficial fungi called mycorrhizae (fungus/roots) which aid in the uptake of nutrients such as phosphorus and zinc, and this ability is not reflected in a soil analysis. A leaf analysis integrates everything the tree is "seeing" – weather, soil, in-tree storage, water, crop load, disease – which is then reflected in the leaf analysis.
Leaf analysis is done at this period, because the leaf nutrients are somewhat stabilized. Young leaves are high in such nutrients as nitrogen and potassium, but low in zinc and iron. As the leaf matures it loses nitrogen and potassium, but gains in iron and zinc. A fully expanded four-month old leaf from the spring flush taken at this time of year has been found to best reflect the tree’s nutrient status. For a discussion on leaf sampling, see our fall 2003 edition of Topics in Subtropics - http://ceventura.ucdavis.edu/newsletterfiles/Topics_in_Subtropics3707.pdf.
If leaf nutrients are low or high, it can indicate not only what nutrient is the problem, but also what sort of corrective actions should be evaluated. It may not be the lack of something like iron, but waterlogging from too long or frequent irrigations. Waterlogged soils reduce iron uptake, and this deficiency might be better addressed by correcting the irrigation practice than spending money on iron applications. Zinc deficiency might be a result of root rot killing root hairs that take up zinc and addressing the disease issue is going to have a longer term improvement on tree nutrient status than simply applying zinc fertilizer. And then of course, if leaves are showing toxicities to sodium or chloride, correcting irrigation leaching and infiltration issues is the way to solve this nutrient problem, since this the easiest way to solve the problem.
This does not mean soil and water analyses are not important, on the contrary. A pre-plant analysis for water and soil can tell you before hand what you might be dealing with and allow you to correct the problem before planting. A high pH is best corrected before trees are in the ground. Trying to correct a zinc, iron, manganese, or copper deficiency with the trees in the ground is expensive and can take years to correct. It is easier to apply sulfur or sulfuric acid to the ground before planting and can be done relatively quickly without harm to the trees. The micronutrient availability is controlled by pH and once soil pH is in the 6-7 range, it is less likely for these deficiencies to occur. Trying to lower pH when the trees show iron deficiency, must be done slowly, since adding too much acidifying material at one time can kill the tree and during the process of acidification, some sort of stop gap measure, such as foliar feeding or fertigation must be employed until the soil pH has slowly been corrected. A water analysis too can forewarn you if you will be having problems with such things as high salinity, chloride, sodium, magnesium, boron or pH, and allow you to select appropriate rootstocks tolerant of the problem or again address it with soil amendments pre-plant.
A soil analysis in conjunction with water analysis can also be used for an ongoing determination of how well irrigation is being managed. Soil from trees doing poorly can be analyzed to see if adequate leaching is being accomplished with the frequency and amounts being applied. Generally, though, a soil analysis is a poor indicator of guiding a tree nutrition program and as an ongoing practice should be used for identifying the toxicity problems of salinity, boron, sodium, chloride and pH.
![S-AV-CULT-IR[1]](https://ucanr.edu/blogs/Topics//blogfiles/18095_original.jpg "S-AV-CULT-IR[1]")
- Author: Ben Faber
UCCE Farm Advisor Gary Bender finally has his 14 chapter book on avocado history, botany and cultural practices on the San Diego County web site. Check it out:
http://ucanr.org/sites/alternativefruits/?story=237&showall=yes
- Author: Ben Faber
Iron chlorosis is an off duck. Soil is basically iron with some aluminum, silicon and oxygen added in for good measure, but plants can lack for iron because it is not available to be taken up. This is often because the soil pH is high due to carbonates which tie up the iron, causing it to precipitate. Another cause is asphyxiation of the roots from too much water. Avocados are especially sensitive to asphyxiation and will show classic interveinal chlorosis and as time goes on, the leaf will turn almost white. They will also show tip burn, like chloride damage in some cases, along with the yellowing. The image of the tree below is of an avocado in a loamy soil with a pH near 7, but is irrigated every two weeks with about 400 gallons of water – kind of boom and bust. The trees are drowning and showing classic iron chlorosis symptoms, but they could also be confused with root rot.
