Avocados in Spring - 1996
April is a transition month from the winter to the summer. Depending on the rainfall, we may be in full irrigation swing or there may still be occasional showers that keep the pumps quiet. Whatever, the irrigation system should be ready to go into action. This is the time of year when we begin to see Santa Ana conditions showing up which can rapidly deplete moisture in the root zone. If there is a bloom that has set with BB- sized fruit, it is quite easy to lose the fruit at this stage to water stress. So make sure the irrigation lines have been flushed of accumulated debris and bacterial slimes, that emitters are working and have uniform emission, that pumps and boosters have been serviced, and the tensiometers have been properly serviced.
By this time the threat of frost has passed, now is the time to get frost equipment repaired. Sometimes parts need to ordered and getting this work done early ensures that equipment will be ready when needed next winter. For those who have been stung by the frost, remember a tree will transpire water in proportion to the amount of leaves present. As the trees put on new leaves (and most will), irrigate according to the amount that is progressively added. This means changing your irrigation frequency and not the amount applied at a given irrigation, if this is possible. This is because most roots are intact from the freeze and their rooting volume is still the same. The soil moisture reservoir is still the same. What has changed and will be changing is the rate at which this water is being pumped out by the leaves. Use the soil auger or shovel to see how much moisture is remaining.
Starting in March, this is a good time to begin a replant program. If possible, it is best to avoid interplanting young trees with older ones. The different watering needs of the two often result in stressed young trees. Try to isolate areas according to irrigation lines or blocks where both young and old can receive the proper irrigation amounts. This is also the time when top working is most successful. If you are trying to introduce new pollen source into the grove for your Hass or are dissatisfied with the performance and marketability of another variety, the cooler weather and the slipping bark usually gives the best graft during the spring.
With young trees, pocket gophers can be especially difficult. With soils moist from rain, they can more easily tunnel and mound. Root and trunk girdling can be a major problem, as well as spread of disease such as Phytophthora citricola. There are mechanical gopher bait applicators, as well as hand application of baits and traps. Continuous checking a prompt control are important, since their populations can climb quite rapidly in the spring. knock down mounds as soon as you see them so that you have an idea of how successful your control program is.
Take a good hard look at the fruit on your trees. How much is there? If you have great fruit clusters, think seriously of doing a size pick. There are any number of ways of playing the harvest game, but if there is a large number of fruit present with the current bloom, the tree is going to be stressed. Large clusters also mean a good hiding place for greenhouse thrips. With the mild winter, there is going to be more likelihood of thrips problems this year. Size picking with an eye on reducing cluster size will discourage thrips numbers. On the other hand, if current fruit number is small and the grove is in need of thinning, get cracking. There is never an ideal time to do this chore, but with fewer fruit, some growers can more easily justify thinning at this time.
April is a month in which short term decisions, such as weed management and foliar zinc nutrition are considered as well as long term ones, such as orchard thinning and cover cropping of a young orchard. This is the nature of a permanent crop like avocado, deciding now what will happen tomorrow, as well as five years from now.