- Author: Ben Faber
I was recently in an orchard looking at what appeared to be avocado root rot. I was checking on the symptoms and quizzing the grower on the other cultural practices. The grower was prepared with soil, leaf and water reports. I asked how much nitrogen was being applied and it was something in the 50 pounds nitrogen per acre. When I saw the water report it listed nitrate in the water at the level of 84 ppm. Rarely do you see a yield response in plants when soil nitrogen exceeds 90 ppm nitrate. The soil nitrogen would pretty rapidly take on the nitrogen level of the water. So this grower was very close to the level at which no yield improvement would occur, and in fact would be increasing vegetative growth and hence increasing pruning problems. I looked at the leaf nitrogen levels and they were quite high, as well. I suggested that it would be a good idea to cut back significantly the amount of fertilizer applied, if not stopping application all together. There are many areas along the coast where avocados are grown where there are high nitrates in the water. Water can be a significant source of nutrients, as well as toxics, such as boron, chloride, sodium and total salts. Learn to read all your reports – soil/leaf/water – and figure out the puzzle of fertilizing appropriately.
- Author: Ben Faber
Amazing. I was out with the contractor who has been doing the California Avocado Commission's annual acreage report. In the past, aerial photography was used and with painstaking accuracy the acreage was visually evaluated by hand. It was so expensive and took so long, that only parts of the California acreage were done each year. The company now uses satellite imagery and computer evaluation to do the whole avocado growing area each year and at much less cost. Now the contractor is going to try to estimate the amount of root rotted acreage that is out there. They will do this by canopy color and texture relative to healthy trees. We were out looking at the range of diseases out there that could be confused with root rot, such as bacterial canker, blight, black streak and crown rot. This will be amazing if they can distinguish amongst the diseases, but even if they can identify unhealthy groves that will be an amazing feat.
- Author: Ben Faber
I got a call yesterday about yellowing avocados. They are on Dusa rootstock which is very tough when it comes to root rot, but cannot handle wet feet. It turns out that this area is one where the grower cannot order water on demand, but must take it when the water company will deliver. So the poor trees get drowned and then go through drought. This sensitive rootstock is not the right one for this area. Many of the root rot resistant rootstocks have some sensitivity to salt, wet, crown rot, whatever, which brings up the question, if we have phosphites, what about the old rootstocks? Barr-Duke, Duke 7 and Borchard have some very attractive qualities: they are tough and can handle things like salinity and drought and are good producers in the absence of root rot. With phosphites now, they can muscle through root rot. Should we reconsider them? Of course, if you are an organic grower, you need to stick with the most root rot resistant selections. And it is also important to remember that the best line of defense against root rot is proper irrigation, which is the leading problem for root rot.
- Author: Blake Sanden
At first thought this sounds like a dumb question. Of course we need to schedule irrigations … just like we schedule lunch; we get hungry, plants get thirsty. End of story. But how many of you skip lunch, or delay it? How often? If you’re like some of us old agronomists that can’t jump across the head ditch as easily as we used to and you look down and can’t see as much of your feet as you did when you were 25 then you think, “Probably better if I skipped lunch anyway.” Then you think on this idea even more and you say, “Well, I just ain’t gonna eat anything until I see this gut disappear.” But we all know this is bad idea as we still need balanced nutrition regularly even if we do have some extra weight.
So before you think I’m completely out to lunch – here’s the connection: if you don’t irrigate until you see the crop stress you’ve waited too long. If you just keep irrigating every three days with microsprinklers (Hey, that’s a schedule, right!?) from May to August without checking the soil/plant water status it’s like eating that foot long sub sandwich every day for lunch and never stepping on the scale! Neither extreme is healthy for you or the crop.
In many ways the San Joaquin Valley has already been placed on a forced diet. A combination of hydrologic and “judicial” drought (The latter being restrictions of State and Federal Project pumping out of the Delta due to Endangered Species Act listing of the Delta Smelt) has drastically cut the import of fresh water to the SJV over the last 3 to 5 years. Growers and water districts have responded by pumping more groundwater, buying “emergency pool” water and other market trades, improving field irrigation efficiency where possible and finally reducing applied water when they just don’t have enough. Now, more than ever we need to know how to use available information and technology for optimal water use.
Process & Planning |
Okay, so I need more than just a calendar to do the best job of irrigation. But what’s this “scientific” thing? Does that mean I have to have a bunch of sensors, loggers and all that stuff? Not at all. In fact, the dictionary meaning of science is NOT ‘using a bunch of gizmos/technology’ but defined as: “systematic knowledge of the physical or material world gained through observation and experimentation.” Wow, sounds pretty close to the definition of a good farmer! Being scientific simply means being consistent in how you record and analyze your observations so that you can develop a system for making the best decisions. This is where gizmos/technology are helpful, as they are tools to collect and analyze data/observations. Some of the most useful gizmos are strictly mechanical.
You can actually do scientific scheduling with no electronics at all; just your hands, a soil probe/auger, regular walks through the field, a notebook and a flometer or weir to record your actual applied water. This was all we had 40 years ago. You don’t even need a computer in the office! But most of us are farming too much acreage to know each field this intimately and we get tired of pounding/twisting soil probes and augers down to 5 feet.
This is where electronic sensors, loggers and automated computer programs are helpful. These devices will automatically collect the data and can do the number crunching that saves you a lot of hand calculation. The only problem is that they’re dumb. They don’t think, they’re usually stuck in one location without the ability to “look around” at the rest of the block. Thus, it’s possible to do “technified” irrigation scheduling (this is the term they like in South America) with all this technology without it being truly “scientific”. In other words, you can collect a whole bunch of numbers but it’s still up to the grower/manager to take those numbers and trends and turn it into systematic knowledge for truly optimal scheduling.
Threre are multiple factors that need to be accounted for if you are going for top field performance - water quality, infilitration rate, rooting depth, drainage, etc. This looks complicated, but in reality most of these are fixed at the time you plant the orchard. Once you determine your soil water holding capacity and irrigation system design application rate, these will be fairly constant. Then the only in-season things that may vary and should be monitored are salinity in the rootzone and irrigation water (How good or bad is it?), soil/rootzone water content (How much is available, how fast are the plants using it?), irrigation frequency (How often?) and system uniformity (How even are my pressures, how often to flush hoses?) The salinity/quality factors are usually tested/treated once a year, unless you’re injecting gypsum and/or acid. So once you’ve processed this data and planned the likely field logistics (i.e. vary irrigation hours to match daily/weekly need or vary onset of irrigation to match a set application say over 24 hours) it’s just a matter of matching the volume water balance pieces together so you can …
These data can be put into a table or even one line of an Excel spreadsheet. You wouldn’t think of buying a booster motor for your pump that didn’t have the boiler plate specs on the casing. But after 23 years of tromping the fields of Kern County I am still surprised by the number of growers and fields that don’t have this simple yet critical information ready and easily accessible.
Using this information along with expected “normal year” ET it’s relatively straightforward to construct a simple water balance checkbook like the one below (which will be available at the workshop).
There are plenty of irrigation scheduling aids/programs on-line. A Google search of “free irrigation scheduling programs” returns more than 80,000 hits. The list will make your head hurt – even before you start to use them. Links to a few of these sites that I have looked at and can recommend as completely free and sponsored by worthy organizations are below:
http://www.cimis.water.ca.gov/cimis/infoIrrSoftware.jsp - Concise list of free and pay-for scheduling software. Some tutorials on basic scheduling. State of CA, Sacramento.
http://www.wateright.org/ - Checkbook type schedule, all on-line, mostly crop water demand based on CIMIS weather and standard crop coefficients. Cal State Fresno, CATI.
http://biomet.ucdavis.edu/irrigation_scheduling/bis/BIS.htm - Multi-worksheet Excel file, completely downloadable, soil moisture estimation but no feedback adjustment. Most comprehensive list of crop coefficients. Calculator for estimating daily crop coefficients. Rick Snyder, UC Davis.
http://cesanjoaquin.ucdavis.edu/files/14724.xls - Simple one-page worksheet checkbook for winegrape irrigation scheduling.
http://oiso.bioe.orst.edu/RealtimeIrrigationSchedule/index.aspx - Most complex of the extension type web-based scheduling programs. Has the capacity to create integrated whole ranch schedules. Difficult to use, but with some of the best “feedback” calculations.
- Author: Mark Hoddle
Avocado leaves infested with trioza was intercepted in March at the San Diego/Mexico border. Avocado leavers are used to wrap tamales. Trioza infested leaves make a tastier tamale.
Introduction
Figure 1. Adult Trioza on a Hass avocado leaf. |
Four species of Trioza are currently known to attack avocado foliage and nymphal feeding causes some form of leaf deformation. Trioza anceps Tuthill is associated with avocados throughout Mexico and Central America. Trioza perseae Tuthill has been described from avocados growing in Peru, and Trioza aguacatae Hollis and Martin and Trioza godoyae Hollis and Martin are known from avocados in Michoacan Mexico, and San Jose Costa Rica, respectively (Hollis and Martin 1997).
All four Trioza spp. appear to have an extremely restricted host range and have only been recorded from leaves of avocados (Persea americana). Further, under some circumstances certain Trioza species (e.g., T. perseae) may even be restricted to particular races of P. americana, which is suggestive of extreme monophagy and host specialization (Hollis and Martin, 1997).
Trioza species have been found on smuggled avocado plants intercepted in San Antonio and Brownsville in Texas, and San Diego in California (Texas and California are states in the USA) (Hollis and Martin 1997). Currently, none of the four Trioza species known to attack avocado leaves are present in the major avocado growing states of the USA (i.e., California, Florida, Texas, and Hawaii). However, given the relatively close proximity of Mexico to California , the high daily volume of tourism, traffic (road, rail, sea, and air), and trade across the California-Mexico border, and the potential for illegal movement of plant material through these identifiable conduits, Trioza anceps and T. aguacatae have high invasion and establishment potential should they be illegally moved on avocado plants that are introduced into California. Consequently, Trioza species represent a serious biosecurity risk for California (the largest avocado producing region in the USA at ~65,000 acres), and other minor avocado producing areas in the USA (especially Texas and Florida).
Around 58 species of psyllids (~2% of described species) are associated with host plants in the Lauraceae, the plant family to which avocados belong. The majority of these psyllid species, ~72% of them, belong to the family Triozidae which contains the genus Trioza, of which ~64% cause some type of leaf deformation to their lauraceous hosts (Hollis and Martin 1997).
Pest Identification and Biology |
Adult Trioza. Trioza species adults are small (~3mm in length), winged, and depending on the species, coloration is either pale green or brown with ochraceous markings. Forewings are hyaline with pronounced veination that may be useful for species identifications. Adults have been observed feeding on avocado leaves, presumably imbibing phloem. Female Trioza species probably oviposit eggs into young avocado leaves by partially inserting them into leaf tissue with the ovipositor. Virtually nothing is known about the basic developmental and reproductive biology and ecology of Trioza species associated with avocados and these are important areas of research in need of attention.
Trioza nymphs. Nymphs are the life stage responsible for causing characteristic deformaties to avocado leaves. Trioza species normally have five nymphal instars before molting to the adult stage. Female T. anceps, T. aguacatae, and T. godoyae apparently lay eggs on the underside of young tender avocado leaves. Nymphs of T. anceps and T. aguacatae upon emerging from eggs create a "pit" within which they commence feeding. As nymphs mature, they induce the formation of protective galls within which they feed. Galls are typically conical vertical growths of leaf material that form on the leaf surface opposite to which the feeding pit is initiated. Typically this is the upper leaf surface for T. anceps and T. aguacatae. T. perseae nymphs apparently feed in pits on the upper leaf surface which then causes gall formation on the lower surface of the leaf (Hollis and Martin 1997). T. godoyae nymphs do not form projecting galls, instead nymphs of this species cause the edges of leaves to roll and feeding occurs within these protective structures (Hollis and Martin 1997).
Very little, if anything, is known about the physiology of gall induction by Trioza species associated with avocados, how nutrition is acquired from within galls, factors influencing development (e.g., temperature, avocado race, leaf age, exposure of leaves to sun and shade, and densities of nymphs and galls per leaf).
Feeding Damage |
Nymphal Trioza spp. induce galls that either develop on the upper or lower leaf surface, or they cause leaf margins to roll. The type of leaf damage observed on avocados is dependent on the species of Trioza infesting the plant. Trioza anceps and T. aguacate cause galls to develop on the upper leaf surface, T. perseae induces gall formation on the lower leaf surface, while T. godoyae infestations result in leaf margins curling.
Attacks by Trioza magnoliae on redbay (Persea borbonia) appear to more intense when plants are shaded, and galled leaves tend to be smaller, senesce more rapidly, and shoots with galled leaves grow less in comparison to shoots lacking galled leaves (Leege 2006). These field observations of T. magnoliae on P. borbonia suggest that gall induction negatively affects plant growth and reproduction (Leege 2006). Consequently, it is possible that Trioza species attacking avocados have similar negative impacts on this host plant. Therefore, it is not surprising that reports from Mexico indicate that heavy Trioza sp. infestations can cause premature leaf defoliation which reduces avocado fruit production (Ebeling 1950, Hernandez et al., 2000).
Natural Enemies as Biological Control |
There are no readily available published records on the natural enemy fauna associated with Trioza species that induce galls in avocados. It is likely that there are specialist hymenopterous parasitoids attacking Trioza nymphs within galls that await discovery in countries with endemic Trioza species. Discovery, identification, and study of these parasitoids, should they exist, could be very important for developing IPM programs in areas with naturally-occurring Trioza species. Knowledge of these natural enemies could be invaluable for future biological control programs against invasive Trioza species in countries with avocado industries that currently lack this pest. Adult Trioza are probably opportunistically preyed upon by generalist natural enemies (e.g., lace wing larvae, spiders, and coccinellids) on avocados.
Many species of psyllids are known to have parasitoids (e.g., Hymenoptera: Eulophidae) that attack nymphs. Some species of invasive psyllid attacking agriculturally important crops has been subjected to classical biological control (e.g., Asian citrus psyllid, Diaphorina citri in Florida with Tamarixia radiata (Waterston) [Hymenoptera: Eulophidae]). Invasive pest psyllids attacking landscape ornamentals have been controlled with specialist natural enemies also (e.g., Eugnenia psyllid, Trioza eugeniae, has been suppressed in parts of California with Tamarixia sp.).
/table>/table>/table>/table>