March Is a Good Time to Evaluate Tree Health and Cultural Management
The most important time of year for California avocado growers is spring, or bloom-time. The fruit-set following bloom that will determine the financial future of the avocado grove the next harvest season. If an avocado grove is currently carrying a second good crop in a row, it is possible the new fruit-set could be poor as the trees become “tired” and enter into an alternate bearing pattern.
The amount of flowers on the avocado trees in spring is thought to be directly related to the amount and quality of the previous year’s summer flush, and it can be moderated by the crop load the trees have carried through winter. Thus, by spring it is too late to have any effect on the amount of flowers the trees will produce. For avocado trees that were affected by freezes in winter, there could also be some flowering potential lost due to flower bud damage. In spring it is possible to see the flower buds on the trees, and it is a good time to consider the avocado grove cultural management activities for the next three to four months.
Comparing avocado flowering and shoot growth
Critically evaluating your trees in March each year is a good practice that allows assessment of how successful your cultural management program has been. At this time of year the amount of fruit to harvest this season can be estimated, and the flowering and fruit-set will indicate crop potential for next year. In order for there to be good fruit-set it is necessary for the trees to flower well. Less flowering and greater shoot growth than expected suggests a light crop could be set, while more flowering and less shoot growth suggests a heavy crop may be set. Depending on the amount of flowering and shoot growth, adjustments to the amount of fertilizer and water applied will need to be made.
Assess amount of stress caused by flowering
Another indicator of successful cultural management is the amount of stress that flowering induces in the trees. Trees that flower well and show relatively little stress are likely to be well set-up to have a good fruit set. If the flowering looks weak or is less than normal this can be an indication a change in avocado grove cultural management practices was needed last year to avoid the poor flowering. The most common cause of poor flowering is a heavy crop of fruit that reduces the amount of flowers that develop, which is the root cause of alternate bearing. Sometimes the crops have been so heavy that two years of poor flowering and yields can result as the tree finds its "balance" between vegetative growth, fruiting and flowering again.
Preventing a small avocado crop yield after large crop yields
In a year where there are two large crops in a row there is a high potential for a poor crop to follow. A good general practice is to ensure the trees have met the nutrient targets for good yields, the overwintered leaves are in good condition (green not yellow) for as long as possible during flowering and fruit set, and to harvest a proportion of fruit from the trees early. If you think your trees look unhealthy or unthrifty talk to your farm advisor about potential cultural management activities you can undertake to best support your trees over the next year. Experience tells us that doing nothing to help unhealthy or unthrifty trees now and over the next couple of months during fruit set is not helpful in setting a good crop.