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Ultrasol® and Speedfol™ B SP help to control plant vigour

In Mexico, around 127.000 hectares are under avocado. The predominant variety is Hass, and there is a strong move to high density planting. In intense orchards, vigour control is a significant challenge to ensure that overcrowding does not quickly occur and to sustain high cropping levels. Fruits are consumed locally and are exported mainly to the USA.

Unlike mango and litchi inflorescences, set fruits on avocado inflorescences do not inhibit vegetative growth from adjacent lateral buds. New growth also emanates from the inflorescences themselves after flowering and initial fruit set (indeterminate inflorescences). Strong, post-flowering new shoot growth is often accompanied by excessive fruit drop, due to the competitive influence of the new shoots. In most circumstances plant growth vigour is controlled by using growth regulators such as uniconazole and paclobutrazol.

Hass avocado
Figure 1. Mario Berrios (Product Manager water-soluble SPN products, SQM Mexico) with the orchard manager (right) in a 4x3 m spaced Hass avocado orchard in the Colima Region, Mexico.

Every year, top and selective side pruning during the non-bearing post-harvest period is required to keep the trees from overcrowding in the orchard row and to prevent the root systems from becoming large. Selective side pruning entails the cutting back of only the branches that have grown further into the orchard inter-row than desired. Hedgerow growing is recommended, and is practiced in the most intense situations. It is also essential that both sides of the hedgerows remain exposed to direct sunlight during most of the day, and that the orchard inter-row is kept open.

Ultrasol® and Speedfol™ Help to Control Plant Vigour in High Density Avocado Orchards.

Pruning date is critical since it affects the stage of shoot maturation at flowering time. Immature shoots fail to flower, and if pruning is carried out too early, new flush development may occur before the general time of flowering which in turn is unfavourable for flowering. Locally carried out trials are to determine the ideal time to prune the trees. In high density avocado orchards, vigour control measures should only be implemented once the trees are close to filling or have filled their allotted space in the orchard row. The time frame can be short, 2 to 3 years after planting in orchards where the inter-row spacing is 4 to 5 m and the inter-tree spacing in the row is 2 to 3 m. soil applied rates of 30 to 50 ml of paclobutrazol may be required per tree to adequately promote flowering since spraying paclobutrazol is generally less effective as a result of leaf runoff.

Uniconazole, spray applied along with Ultrasol® K during flowering, is effective to prevent excessive fruit drop and to increase the average fruit size, since small fruit size is a general problem in Hass and often related to ovule longevity after fertilization. 1 spray with uniconazole followed by 2 sprays of only Ultrasol® K (2% w/v) are recommended for best results. Soil pH is often high (> 7,5) and manifestly reduces the tree’s ability to take up essential trace elements such as Cu, Fe, Mn, Zn and B from the soil. In this case, adding chelated trace elements to the spray tank is recommended. Application of EDTA Zn, Mn and Cu, respectively at 300, 250 and 100 g per 100 l, EDDHA Fe at 500 g per 100 l, and Speedfol™ B SP at 300 g per 100 l is suitable.

Date of Sampling
Figure 2. Avocado trees grown on calcareous slopes in the Colima region, Mexico. The soil is ridged to enhance drainage and to limit Phytophthora root rot which is favoured by prolonged soil wetness. Irrigating with sulphuric acid at 400 ml per 1.000 l of water is recommended to remove sodium from the root zone. Spraying Ultrasol® K Phite SL is recommended as an aid to fight Phytophthora root rot.

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