- Author: Ben Faber
Armillaria mellea is the pathogen that causes root rot of many forest and ornamental and agronomic trees. The pathogen occurs in landscapes and urban soils as well as a natural pathogen in forests and on lands converted to farming. While symptoms can appear suddenly, it is generally considered a slowly developing pathogen that takes years to kill a tree. When infected trees begin to die and are removed from orchards the fungus rapidly colonizes the remaining roots and resides in soil as potential inoculum for trees planted later.
Armillaria is difficult to control. Fungicides are not effective and even the most effective fumigants such as methyl bromide may not completely eradicate Armillaria from soils. Sterol demethylation inhibiting fungicides can be effective in slowing and preventing Armillaria infections in grape and stone fruit crops. Fungicides if used frequently are subject to breakdown in effectiveness through pathogen resistance to the treatment.
Adding uncomposted organic matter to soil provides the carbon and energy necessary to build microbial populations in soil, some of which are antagonistic to Armillaria. Mulches of bark and fresh woody debris of Scots pine increased soil microbial activity and organisms (fungi) eleven years after treatment. In this study both Trichoderma koingii and fresh wood and bark mulches applied to soil increased T. verde. Tree wood products such as yardwste or tree trimmings wastes are effective substrate for culture of many different fungi including Trichoderma spp. Downer et al, found that Armillaria mellea only survived a maximum of 11 days in fresh yardwaste static piles and that recovery of viable Armillaria was negatively associated with increases in Trichoderma in the wood chips.
Trichoderma have long been understood to play a role in control of Armillaria, especially after soil fumigation. Some effectiveness has been shown with Trichoderma in concert with other non-chemical methods.
In this study two potential cultural controls (hole size and yardwaste amending) and one biological treatment (Trichoderma application) on their ability to help peach trees survive Armillaria infested soil.
Peaches, Prunus persica were planted as grafted saplings in an avocado orchard previously infested with Armillaria mellea (Vahl) P.Kumm. Peaches were used because they are so sensitive to the fungus. Trees were planted in large or small holes withor without fresh yardwaste chips added as an amendment and with or without a Trichodermabiocontrol product sprayed into the hole. Trees were monitored for six years -- growth and mortality was tabulated. Six years later 40% of the trees had died from the disease. Trees planted in a large hole were more likely to survive than in a smaller hole (P=0.07) and trees in large holes with fresh organic matter added were the most likely to survive (P=0.04). Trichoderma sprays in the planting hole did not increase survival rates. While growth was initially retarded by adding fresh yardwaste to the hole, in later years none of the treatments affected growth rates
Read on: https://www.plantsciencejournal.com/apdf/jpsp-aid1031.pdf
- Author: Hamutahl Cohen
How the new neonic regulations impact your operations
There are new neonicotinoid regulations effective starting Jan 1, 2024 to protect pollinators. Neonicotinoids are a class of pesticide that are chemically similar to nicotine and that affect insect central nervous systems, resulting in paralysis and death. They are known to negatively impact pollinators, including bees. Neonicotinoid pesticide products include the active ingredients clothianidin, dinotefuran, imidacloprid, and thiamethoxam. The new regulations affect the applications of these pesticides on some crops. Because pesticide labels will not be updated, it is critical that anyone using these products is aware of the regulations.
For crops that are harvested after bloom (e.g. berries, citrus, cucurbits, oilseed crops, pome fruits, stone fruits, tree nuts), neonic use is prohibited during bloom. In addition, there are restrictions that apply if multiple active ingredients are used OR if both soil and foliar applications are used during the growing season. These restrictions are concerned with the application amounts of the active ingredient and vary by crop type. There are also additional restrictions if managed pollinators are being used. Because there are additional restrictions for certain crops, the best way to understand how your crop will be influenced is to examine the regulations for each crop at this site, which has crop-specific factsheets: https://www.cdpr.ca.gov/docs/enforce/neonicotinoid/neonicotinoid_regulations.htm
There is another category of crop, those for which DPR determined that neonic applications might impact pollinators. This crop category includes avocados, figs, coffee, peanuts, and dates. For these crops, neonic use is prohibited during bloom. In addition, only one neonic active ingredient is permitted during the growing season, and one application method (foliar or soil). Neonic use is also prohibited on these crops when managed pollinators are used during the growing season.
Let's talk about which crops are NOT impacted. Those crops that are harvested before bloom, such as herbs, leafy greens, and bulbs (e.g. garlic) are not subject to the new regulations, and growers can still apply neonics according to the current label. Crops that are grown in enclosed spaces (e.g. greenhouses) or under insect structures (e.g. netted blueberries) are exempt from the new regulations.
There is another scenario that is exempt from the regulations -- any applications to crops to control a quarantine pest. This means that any application to control a quarantine-listed fruit fly or Asian Citrus Psyllid (ACP) are exempt from regulations. Let's talk about what this means for a lemon grower in Ventura County. Under the new regulations, they should not apply any neonics while the crop is in bloom, even if only a few flowers are open. This means no neonic applications for much of the year. However, a grower can apply neonics to their lemon bloom AT ANY TIME, including during bloom, if ACP is the listed targeted pest. To achieve this exemption, the grower must obtain a written recommendation from a licensed PCA for the ACP application, and they must keep this recommendation for two years.
If you have questions about the new regulations, feel free to contact me at UCCE Ventura County at hcohen@ucanr.edu.
- Author: Ben Faber
The California Farm Conference has been going on for 36 years, sponsored by a variety of organizations over the years- CA Alliance with Family Farmers, UC ANR Small Farms Program, USDA and others. This year, CAFF and a wide range of other organizations have jumped into lead the meeting(s). Plural? In the past, it was held at one site over several days, either north, south or central California. Now, events are at multiple sites and during many times, in--person and in-digital. Lotta speakers on a lotta topics applicable to a lotta growing environments. Check it out:
https://casmallconference.sched.com/
And on Thursday, February 29, 2024, one of the events will be in Fillmore
/span>- Author: Ben Faber
Plants, therefore avocados, go through different growth stages, so called phenological stages, regular periods where they grow and differentiate from seed to various vegetative stages, flowering and finally seed production. Avocado has a preset pattern of phenology that occurs depending on variety and where it is grown, driven by light, temperature, water availability and often by different stresses, such as cold, heat, and heavy or light crop load.
Differences in crop development impact the timing of cultural practices, such as fertilization, irrigation, phytophthora treatment, pollination and gibberellin sprays. For instance, nitrogen fertilization is often recommended by month of the year, rather than growth stage of the tree. Several recent efforts indicated that the timing of nitrogen fertilizer may have significant impacts on yield and that two times the fertilizer rates in April and November may result in substantial yield increase. Available information indicates the April timing might correspond to fruit set for the Irvine area compared to early bloom for Santa Barbara and San Luis. By November, Irvine's current year's crop may have been harvested three months previously. In San Luis Obispo, harvest may have just ended. So just going by date is insufficient for guiding many horticultural activities.
California's trees often have two crops maturing at the same time. It becomes especially pronounced the further north the production. The management of multiple crops on each tree becomes more important and more confusing as the length of time the fruit remains on the tree. Carrying two and even three loads of crop increases the potential for alternate bearing. Reduction in alternate bearing has been determined to be an important strategic requirement for California's growers. Understanding the impacts of cultural practices on alternate bearing is important. For example, the chart below demonstrates a stylized calendar of the avocado growth cycle for California. Rate and application timing of nitrogen as predicted by the Avocado Nitrogen Model proposed by Rosecrance et al. (2013 and Calculator) are noted for a 15,000 per acre yield outcome. The “on” year suggests nitrogen rate for the late fruit growth/harvest/summer and fall flush period is 15 lbs. This application coincides with the fruit set timing for 16 lbs of N for the “off” bloom crop during the later bloom/fruit set/spring shoot growth phase. Rates and timings to support these crops ought then be combined and represent the 2X fertilizer rate that Lovatt (2001) found to have significant effects on yields.
Taking into account the actual phenology, what is happening in your trees, then is important for assessing when to make N applications. In the winter and spring of 2023, it seems like everything was on a different cycle. Thrips delayed their appearance, flowering was erratic. Honeybees seemed to have found somewhere else to hang out, because they were not flying in the avocado trees. And then suddenly, we had some fruit set in Ventura in late June. This is a really clear example of the problem of following a cookbook to farming avocados. The point here is that just going by the calendar is not going to meet the needs of the tree. The phenological stages of the tree in your environment needs to be taken into consideration.
Notes:
Lovatt, C.J. 2001 Properly Timed Soilapplied Nitrogen Fertilizer Increases Yield and Fruit Size of ‘Hass' Avocado. J. Amer. Soc. Hort. Sci. 126(5): 555?559.
Rosecrance, R., Lovatt, C.J., 2013. Management tools for fertilization of the 'Hass' avocado. FREP final report.
Calculator: https://rrosecrance.yourweb.csuchico.edu/Model/AvoModel/Avo2NKModel.html
- Author: Ben Faber
Most commonly we associate the malformed fruit we see in lemons to citrus bud mite. But it can also occur on other varieties of citrus in Southern California, including in this case to tangelos. If there's enough fruit to bite into, it's still edible.
Citrus bud mite is very small, elongated and somewhat tapered at the posterior end, and has four legs at the front end near the mouth. Look really closely in this image to see the squiggly little thing that can cause so much damage, those little white, hooked shaped things within the larger buds.
Females lay about 50 eggs mostly in the bud scales of recent growth. Mite numbers peak in summer, and summer and fall blooms are most likely to suffer damage.
Citrus bud mite is primarily a pest of coastal lemons but in recent years has also been found in interior regions of Southern California. The mites feed inside the buds, killing them or causing a rosettelike growth of the subsequent foliage and distortion of flowers and fruit, which may or may not reduce yield, fruit quality, or both.
Recent research has failed to show any consistent harm caused by bud mite feeding under oil spray regimes, especially in Lisbon lemons, and bud mite damage is offset by the negative phytotoxic effects of oil. Research has not been done to determine if abamectin plus oil sprays for bud mite are economically justified. To detect bud mites before damage occurs:
- Check buds on green angular twigs from mid-spring to autumn.
- Collect one bud from each of 50 randomly chosen trees throughout the orchard.
- Dissect the buds under a microscope or use a 20X hand lens to determine the percent of buds infested with one or more live mites.
As an alternative to dissecting buds, bud infestation can be estimated from infested fruit buttons.
- Collect one green fruit, about 1.25 to 2 inches in diameter, from 50 trees scattered throughout the orchard.
- Remove the button and record whether the button or the fruit beneath the button is infested with live bud mites. The relationship between fruit and bud infestations is not linear, but a fruit infestation of 15 to 20% indicates a bud infestation of about 45 to 50%.
No bud mite threshold had been established; levels as high as 80% bud infestation have failed to cause consistent or predictable economic losses. If a reduction of bud mite numbers is desired, apply insecticides 2 to 3 months before the bloom that is to be protected.
READ ON For MORE INFORMATION FROM UC IPM
https://ipm.ucanr.edu/agriculture/citrus/citrus-bud-mite/