Author: indexfresh

Avocado growers in California have long grappled with the devastating effects of root rot, a disease caused by the soil borne pathogen hytophthora cinnamomi. This insidious fungus can significantly reduce tree health, fruit quality, and yield, ultimately leading to tree death.

After playing the role of villain in the California avocado industry for decades, P. cinnamomi is finding itself outmatched by a product that hit the market in 2021 called Orondis. A cutting-edge fungicide by Syngenta, Orondis is proving highly effective in controlling root rot.

When our Index Fresh staff presented the 2024 Cultural Seminar Series, they fielded numerous requests from avocado growers seeking more information about Orondis. The following information relies primarily on direct input from Syngenta, as well as experts in the avocado industry.

Why has root rot plagued the avocado industry for so long?

P. cinnamomi thrives in areas of excess soil moisture and poor drainage and can survive adverse conditions as persistent spores in the soil. Avocados didn’t evolve alongside the pathogen, which is thought to have originated in New Guinea, thus never developed resistance to P. cinnamomi. As Farm Advisor-Emeritus Gary Bender pointed out in his recent article in the California Avocado Society’s Avocado Quarterly, “California growers have developed an efficient way to harvest fruit and get it to the packinghouse, but that system also moves the fungus from grove to grove via dirty bins, dirty ladders, truck tires and on the boots of pickers who move from grove to grove.”

How Does Orondis Work?

Orondis, with its active ingredient oxathiapiprolin, operates through a unique mode of action. It targets a specific protein essential for the survival and reproduction of Phytophthora, effectively disrupting its life cycle. By reducing the pathogen’s population in the soil, Orondis promotes healthier root systems, improved water and nutrient uptake, and increased tree vigor.

“Orondis works directly against the Phytophthora propagules in the soil, rather than against the pathogen in the tree, effectively eradicating the pathogen from treated soil for a period following application,” stated Tim Spann in the winter 2021 edition of the California Avocado Commission’s “From the Grove” magazine.

Key Considerations for Orondis Application

Timing: Apply Orondis during periods of root flush, typically in spring and late summer. Note that Orondis has a restricted entry interval of 4 hours and a pre-harvest interval of 30 days.

Method of Application: Soil should be  pre-wetted  before  application. Orondis should be applied through the irrigation water (micro-sprinkler or drip). A general recommendation, using drip irrigation as a guide, would be to allow for at least 6-8 hours (but no more than 10-12 hours of water) to be run after the injection of Orondis.

Rate: Labeled use rates are 4.8 fl oz/A – 9.6 fl oz/A. When establishing a new grove, or for heavy/severe infections, the higher end of labeled rates is recommended on a 6-month retreatment program for the first year. If soil testing confirms a significant reduction in Phytophthora propagules following treatment, you can consider switching to a maintenance program of 4.8 fl oz/A on a 6-month retreatment interval, or 9.6 fl oz/A on a 12-month retreatment interval.

Rotation: Resistance Management guidelines  on  the  Orondis  label instructs growers to limit sequential use of Orondis to two applications before rotating to a fungicide with a different mode of action.

Integrated Pest Management with Orondis

“While Orondis is extremely effective at reducing Phytophthora populations in the soil at low use rates, there is no silver bullet, and incorporating things like cultural controls are also imperative for long-term management of the disease,” states Dr. Jeannette Rapicavoli, Agronomic Service Representative for Syngenta.

Optimal results rely on combining various strategies, including:

Cultural Practices: Help minimize disease pressure by irrigating appropriately (duration and amount), no wetting of trunks, planting on berms, applying organic mulch and ensuring proper tree nutrition Resistant Rootstocks: Using resistant rootstocks can provide a strong defense against the pathogen.

Sanitation: Prevent soil or water movement from infested areas.

Fungicide Applications: Timely applications of Orondis can effectively control Phytophthora.

At this stage of the season, we are completing the flowering and fruit set, a process in which the tree spends a lot of energy (sugars, starch, water, nutrients, etc.). Now is the time to recover all resources used by the tree. Your avocado trees now need: 

Fertilizer: Adjust nutrient amounts based on fruit load and the stimulation of new growth (next year’s floral shoots). Aim to make healthy leaves, fruiting wood, and strong roots. 

Irrigation: Water is the basis of the photosynthesis process (energy for the tree). Increase the amount of water and/ or irrigation frequency. 

Pruning: Control the height of tall trees, regulate alternate bearing, control regrowth, and remove “dead” wood. It is important to keep a good balance between reproductive and vegetative growth. Reduce sunburn by painting the branches with a mix of white paint and water. Remember to disinfect pruning tools between each tree. 

Pest control: Monitor pest populations, such as persea mite, to evaluate need for control. 

Mulching: Add mulch to improve conditions for better root growth.

By Gerardo Aldunate, Agronomist, Index Fresh

Scorching heat across interior Ventura County this July spelled trouble for avocado growers. When the mercury climbs over 100 degrees for days, it can mean total crop loss. Growers across California’s avocado growing region who are vulnerable to high heat have applied old-fashioned farming ingenuity and novel techniques to combat the worsening threat caused by extreme heat. 

“It’s definitely getting hotter,” said Dr. Ben Faber, a farm adviser with UC Cooperative Extension. “Just 10 years ago, 110 degrees was unheard of, and since then we’ve had three summers in Santa Paula and Fillmore when it’s gotten 110 degrees and hotter. It’s gotten to 120. It’s not supposed to happen, but it’s happening.” 

The avocado tree is sensitive to temperature fluctuations in both directions, and the aftermath of heat damage looks a lot like the aftermath of frost. After extreme heat, the orchard needs to be evaluated for damage. Fruit can drop — in severe cases, most of it — and if the leaves start to get crunchy from heat damage, the first step is to reduce irrigation and fertilization. The damaged tree cannot process the irrigation like a healthy tree, so excess water, even from regular irrigation, could lead to root rot on impacted trees. Another tell-tale sign of heat damage is browning of the stem where it connects to the fruit. Avocados with browning stems will eventually drop.  

“Leaves are crispy. The fruit is on the ground. You’ll know heat damage when you see it. It’s really obvious,” Faber said. In the event that the leaves drop, apply whitewash to exposed branches to prevent sunburn. Otherwise, avoid pruning until there is new growth in order to protect the tree from sunburn. 

It could take six months to a year to observe the extent of the damage to each tree, whether it’s a matter of temporary fruit and leaf damage for the season or if the tree is severely impacted and might never recover. 

Beware Of Forecasts Over 90 Degrees 

Finicky avocado trees react to temperatures over 90 degrees. The stomata on the leaves, which open to allow transpiration under normal circumstances, close to retain moisture, but a side effect is causing the tree’s internal temperature to accelerate upward. If the forecast predicts that the temperature at your orchard will exceed 90 degrees throughout the day, consider that as being in the avocado tree heat advisory zone. 

“We’ve had to advise Index Fresh growers on recognizing and preparing for ever-more-frequent extreme heat,” said Keith Blanchard, California Field Manager for Index Fresh. “The good news is there are measures to take that can protect the crop and trees from extreme heat.” 

Faber, a specialist in subtropical horticulture, pointed out that avocado trees are at home in tropical weather, but the tree evolved to live under larger trees in the forest. Cultivators have taken avocados out of their natural shaded setting, so we must apply farming tools to protect them. “Avocado trees were naturally accustomed to hot weather, but also being shaded,” he said. 

Preparing For Extreme Heat 

As they have adapted to extreme heat, growers have developed game plans with mainly two proven techniques, advanced irrigation and overhead sprinklers. 

Overhead sprinklers can reduce ambient temperatures by 10 degrees through evaporative cooling in the orchard. If the forecast calls for 100 degrees, it is possible to bring temps down to about 90 degrees in the orchard, or right at the threshold before the trees close their stomata and enter the danger zone where internal temps spike. 

Even before it becomes time to switch on the overhead sprinklers, growers should prepare by irrigating ahead of time. Trees that are hydrated will withstand greater heat and suffer less damage, even if temps climb over 90 degrees. “Sometimes, the grower says, ‘Oh, it’s hot. I’m going to turn the irrigation on.’ But by then it’s too late,” Faber said. “If you can anticipate it and hydrate the tree, that’s when you are helping, because when it’s too hot, water isn’t going anywhere.”

In addition to overhead sprinklers, growers can reduce ambient temperature through adding moisture and evaporation to ambient air. The added overhead shower is most helpful when the water settles on the leaves or other surfaces, because that water will cool the tree down immediately, Faber said. 

Anecdotally, growers in hot temp zones have been able to install overhead sprinklers for about $1,200 per acre by laying them over existing irrigation systems. Growers will use overhead sprinklers in blocks during heat events, and it is important to monitor and rotate sprinkler locations frequently enough to keep trees moist throughout hot weather. 

Different Results On Different Trees 

Orchards in the same climate can have wildly different outcomes from extreme heat events. A recent event in Santa Paula caused nearly 90% fruit loss at one avocado orchard but others that were nearby withstood temperatures with far less damage. 

“Really, it’s a carpet of fruit on the ground,” Faber said of the badly hit orchards. 

Heartier trees where the fruit sets inside the canopy seem to handle extreme temperatures better. Also, some growers are finding that GEM trees, shaped so fruit sets inside the canopy, tend to fare better in hot or cold temps. The added protection from the elements was a primary reason for selecting the GEM to commercially cultivate. 

Note Of Caution 

Faber advises against using products marketed as Antistress 550/2000 on avocado trees. The products, which are applied to the canopy, can do more harm than good on avocados.

In 2024, even when Mexico is on the sidelines, its nuanced supply chain can greatly impact the U.S. avocado market. The suspension of avocado exports from the state of Michoacán in mid-June caused prices to spike and California growers to strip the 2024 crop as fast as they could. Peru also pivoted shipments into the U.S., chasing the hole left in the market by Mexico. The lasting effect of Michoacán’s timeout has been a disruption to the U.S. avocado market. Prices and supplies were thrown out of whack, and the industry is still waiting for the impact to dissipate. In addition to Mexico and Peru, below we outline key players in the 2024 U.S. avocado market — adding Colombia and Chile —  and the status of their crop this year.

2024 Country By Country Outlook 

Mexico

Status — Mexico has shipped about 1.3 billion pounds of avocados into the U.S. in 2024, compared to about 1.4 billion to date in 2023. This is the second consecutive year that drought has diminished Mexico’s crop. Rain delays in Michoacán, where most avocado acreage is exclusively rain-fed, has greatly impacted fruit size and crop volume. We are watching the development of avocados from the state of Jalisco entering the U.S. According to APEAJAL, Jalisco’s avocado export group, the peak season for harvest this year has been delayed due to drought. Jalisco, which ships about half of its total exports into the U.S., remains early in its development as a major exporter, as it awaits export clearance for more of its orchards. 

Projection 2024 — Overall, Mexico is projected to finish 2024 with a 2.4-billion-pound share of the U.S. market, falling short of its 2023 record U.S. export volume year of 2.5 billion pounds. 

Peru 

Status —  Like California, Peru continues to find avocados on trees that were not included in its preseason projections. El Niño weather conditions in 2023 impacted the 2024 crop leading to the expectation that exports would be severely reduced. That outlook, however, has since been tempered to a 10% reduction year-over-year. So far this year, about 80 million pounds of Peruvian avocados have landed in the United States. Peru shipments peaked in mid-July at nearly 15 million pounds per week into the U.S. 

Updated Projection 2024 — Peru sent 166 million pounds of avocados into the U.S. in 2023; shaving 10% from that would make this a 150-million-pound year.

Colombia

Status — Colombia has grown its avocado exports into the U.S. this year by shipping over 40 million pounds, beating 2023’s total of 23 million pounds. Colombia produces year round but is currently peaking at around 4 million pounds per week. To add context, Colombia never broke 1.5 million pounds in a week in 2023.

Projection 2024 — Like Peru, Colombia is setting itself up for global expansion, and it enjoys easy access to the U.S. East Coast. In 2024, the U.S. is expected to receive 68 million pounds of avocados from Colombia. Though it lags behind Peru in its annual volumes, Colombia is adding producing acres annually. 

Chile

Status — Chile has only sent 300,000 pounds of avocados to the U.S. this year and topped out at 11 million pounds last year. It simply hasn’t been a game changing contributor of avocados into the U.S.

Projections — Chile enjoys a niche season in the U.S., September through December, just after California and Peru typically hang their hats for the season. Chile’s reduced supply and strong domestic demand will divert produce away from export markets. The avocados that do make it to export are most likely to be shipped to the E.U.

This year’s avocado harvest in coastal California has been ravaged by avocado thrips, the little insects that feast on newly set fruit and leave lasting scars. Cold, wet and foggy weather conditions in late spring 2023 are causing 2024’s crop to get downgraded due to the tell-tale tan skin blotches caused by avocado thrips.

“Thrips go after avocados the size of BBs or peas, up to large olives, and just two or three thrips will cause significant damage,” said Tom Roberts, a pest control advisor and own r of Integrated Consulting Entomology. “When the weather Is cold, it takes the fruit longer to size up, leaving it vulnerable to thrips for an extended period.”

This year’s harvest in coastal areas is the most thrips-damaged since the late 1990s, when avocados were first successfully treated for thrips with abamectin.

An (Im)Perfect Storm

Late spring into summer 2023 presented a perfect storm of conditions allowing for pernicious thrips to damage crops. Up and down the coast, cold, wet weather settled in. Conditions grounded applicator helicopters and prolonged the period for thrips to damage the crop.

“Thrips thrive in colder weather, but if it’s too cold, they are less active and less likely to contact treatments like abamectin, commented Roberts. “Even if the helicopters treated the crop for thrips, chilly insects were hidden away, rendering treatments ineffective. Pollinators also were lazy due to the cold, so the fruit set was delayed, extending the treatment window and making it less predictable.”

Cold weather also stunted fruit growth, so thrips outlasted the efficacy of abamectin. Firing up helicopters to treat for thrips a second time in early summer would cost upwards of $20,000, a sizable input to consider for farmers operating on tight margins.

Timing Treatments

Avocado thrips first became prevalent in California in the mid-1990s and wreaked havoc until growers got clearance to apply abamectin to the crop in 1997/98. At 50 gallons per acre, an application of abamectin will treat for thrips and protect the crop. It must be applied during the window when leaf flush is at about ½ to 2/3 of leaf expansion and the fruit is just setting. “Thrips need good leaf flush to build numbers,” Roberts said. Leaf flush was delayed in 2023, which likely slowed thrips population growth, but at the same time provided less surface for the abamectin to collect.

In a typical year, leaf expansion will hit the ½ to ½ mark around the time that fruit is setting. Thrips thrive in this period, when the fruit is so immature it’s still in the sepal, making a little home for the thrips. The insects like leaf flush as well, so they will come out of hiding and contact the treatment on the soft young leaves.

The ideal time for treatment will vary slightly by region and year. Your crop advisor or entomologist will know the best timing for treatment, and it’s important to get on the schedule. Helicopters are a limited resource, which can create scheduling challenges when the thrips window is “a moving target,” according to Roberts. Much of the growing region that is most vulnerable to thrips requires treatment in late May or early June.

Thrips do not like heat. If a heatwave strikes and temps climb over 86 degrees, a crop advisor might recommend holding off on thrips treatment. Heat will take down thrips populations and accelerate fruit growth and push it past thrips vulnerability.

“If the fruit is over an inch in diameter, it takes significantly more thrips to cause visible scarring,” noted Roberts.

Treatment Resistance And Protecting Good Bugs

Hindsight is 20/20, and Roberts notes that timely application of a pyrethroid most likely would have reduced thrips numbers quicker in 2023. Pyrethroids are contact materials that are more deadly than abamectin, but at the cost of also eliminating resident predaceous insects that are needed to naturally regulate pest populations like omnivorous looper and longtail mealybug. Protecting populations of good bugs in the orchard can be as important as timely treatments against bad bugs.

Resistance is another factor in deciding what material to use for thrips management. Insect experts, such as Dr. Joe Morse (U.C. Riverside), observe that thrips will likely develop a resistance to abamectin. Cycling in alternative treatments like sabadilla and spinosad could help to limit resistance to abamectin and assist in the long­ term fight against thrips.

Source: 
TOM ROBERTS, AGRICULTURAL BIOLOGIST; PCA. INTEGRATED CONSULTING ENTOMOLOGY (ICE)