Cultural Practices to Reduce Pest and Disease in Avocado & Citrus

In many ways our pest and disease management of fruit tree crops are exacerbated by our cultural practices. Avocado and citrus offer some very clear demonstrations of how we manage our trees can lead to reduced pesticide use. From the beginning, our selection of rootstock and scion can help lessen pest and disease problems. In both avocado and citrus we have good rootstocks which can handle problems, such as root rot more effectively than seedling rootstocks. So it is imperative that if you know that drainage will be a problem, starting off with the right, healthy rootstock helps. Also scion selection can have a major impact, as well. For example, ‘Lamb' avocado is much less prone to persea mite than is ‘Hass'. This pest can significantly impact a spray program and planting ‘Lamb' could mean virtually no sprays for this pest. Selling the ‘Lamb' fruit is then the challenge There are similar examples in citrus where one variety is more prone to a pest or disease than another.

 

Irrigation is probably the most important cultural factor in managing tree disease. Over, under and improperly timed irrigations are the conditions necessary for many root diseases. The Phytophthora spp. fungi are looking for distressed root systems brought on by waterlogging and other stressful situations. Other conditions, such as wetted trunks can also bring on some trunk diseases, like gummosis in citrus and crown rot in avocado. Simply preventing irrigation water on the trunks can limit these diseases. Other diseases, such as black streak, stem blight and bacterial canker in avocado are bought on by soil moisture stress.

 

Nutrients, especially nitrogen management, has been long known to affect levels of insects, such as scale, mealy bug and aphid. Encouraging lush growth helps sustain these insects, so reducing this growth tends to lower their numbers. Managing when canopy growth occurs can affect pest severity. Avocado thrips build their populations in the spring and moves easily from leaf to fruit causing significant scarring. By promoting leaf growth at flowering time with a nitrogen application, keeps the insect on the leaves and reduces fruit scarring. This also promotes growth that replaces leaves that have been damaged by persea mite. Likewise the incidence of citrus leaf miner damage can be reduced if spring pruning is avoided so that a flush of growth does not occur at the same time as the population is building. Timing of pruning is important in lemons to avoid wet periods of rain and fog to reduce the spread of hyphoderma wood rot fungus when its fruiting bodies are active.

 

Pruning can change pest pressure by changing the humidity in the canopy, introducing light and changing the climate supporting disease and pests. By making spray coverage more thorough, it also makes for a more effective application. Modified skirt pruning can have significant effects on mealy bug and scale control, fuller rose weevil incidence, ant colonization and snail damage. It's important that the trunk be protected as an avenue of movement for snail and ant control to get the best effects of this pruning. Skirt pruning also reduces problems with such weeds as bladder pod and the ladder effect of brown rot in citrus – fungal propagules splashed from the ground onto low-hanging fruit, which in turn is splashed to higher fruit.

 

Keeping a canopy clean of dust and fire ash also makes for more efficient biological control. Because predators are slowed in their search, they are less efficient. They also spend more time grooming their sensory organs, and this also slows them down. Parasites such as wasps are actually slowed by the physical abrasion to their tarsi. Dust also creates a drier environment, which is more hospitable to our pest mites. Watering picking rows, roads and even the trees themselves can lessen mite populations. Use of cover crops can also reduce dust and potentially provide pollen and nectar for predators and parasites. Of course cover crops create a whole new set of management issues, such as colder winter orchards and snails.

 

Finally harvest timing to avoid pest and disease is often overlooked. In avocado, fruit is often set in clusters. Greenhouse thrips love the microclimate created, and if in a size-pick the cluster is reduced, greenhouse thrips will often not be a problem. Harvest timing is also important in citrus. Fruit left too long on the tree can often develop septoria fungal spot. Picking in a timely manner reduces the incidence of this disease.

 

These are just a few examples of how cultural practices at the right time can reduce pest and disease problems.

avocado pruning

An Apple and An Avocado Both Start With

Scholarship Opportunities

We are proposing scholarships for the class each year, which cover the cost of the first week of the course ($1975)

To be eligible for the 2020 Principles of Fruit & Nut Tree Growth, Cropping & Management Course Scholarship you must be:

• A Californian grower
• A new grower with fewer than 3 years experience with tree crops OR in the process of transitioning between crops
• On a small farm with fewer than 40 acres of tree crops

You must apply before November 1st, 2019.

We will review all applications received and notify applicants of our decision by November 30, 2019.

The scholarship does not cover fees not included in the course price, like accommodation and dinners. If you wish to attend the second week as well, you will be responsible for all fees for that week ($1215).

If you have any questions about the scholarship application please send an email to fruitsandnuts@ucdavis.edu

 

Scholarship application 2020

 

 

avocad set painting

Avocado in Southern California - 1911

In 1911, the avocado was a relatively new crop in Southern California and the great USDA plant explorer Wilson Popenoe (pronounced POP e Noe according to Jack Shepherd), describes avocado culture and its problems

https://www.biodiversitylibrary.org/item/137628#page/31/mode/thumb

This is from the first volume ever of the Pomona Journal of Economic Botany which also has a nice description of "wither tip" of citrus in Santa Paula.

https://www.biodiversitylibrary.org/item/137628#page/5/mode/1up

 

Cover Avocado in Southern California - Wilson Popenoe

What's Wrong with My Citrus?????????????

Hats Off.

The Orange County Master Gardeners have lived up to their name with their website information on citrus. It's a truly impressive information site for not only homeowners, but also growers:

http://mgorange.ucanr.edu/Edible_Plants/?uid=108&ds=530

The “Citrus Problem Diagnosis Chart” is especially work perusing:

http://ucce.ucdavis.edu/files/datastore/530-15.pdf

Orange County logo

citrus and mountains

SIX-WEEK AVOCADO PRODUCTION COURSE BEGINS IN MAY

Dr. Gary Bender, UC Cooperative Extension (UCCE) Farm Advisor Emeritus, is the lead instructor for a six-week course entitled “Avocado Production for New Growers.” Co-instructor, Sonia Rios, current subtropical Farm Advisor, Riverside/San Diego Counties will also be teaching in the course. The course is designed for new avocado growers, as well as those interested in learning more about avocado production best practices and meeting fellow growers.

The six-week course consists of six, two-hour sessions and will be held in Fallbrook, CA this year. The fee for the course is $105 and includes two avocado books, an IPM book and a post-harvest handbook. Final dates and the location will be announced soon. The always fills up, so please register A.S.A.P.

Topics include:

• Introduction to Agriculture in San Diego County, History of Avocado Production in California
• Botany, Flowering, Varieties, Harvest Dates, Rootstocks 
• Irrigation Systems, Irrigation Scheduling, Salinity Management
• Fertilization, Organic Production
• Weed, Insect and Mite Control, Disease Control
• Ag Waiver Water School Training (Dr. Loretta Bates)
• Canopy Management, Tree Spacing, Frost Management
• Field trip to High Density Trial grove and a commercial grove

For more information, contact Erin Thompson at 858.822.7919 or enthompson@ucanr.edu.

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