Effect of nets on growth, yield and fruit quality as well economic feasibility in plums

We evaluated several plant growth regulators (PGRs) on plum trees grown under shade net to see whether these can control vegetative growth without any detrimental effect on fruit quality. In addition, we evaluated the effect of shade nets on fruit quality at harvest and after cold storage and shelf-life compared to fruit grown on trees in full sun.

Foliar or soil applied PGRs were made in spring and/or autumn. Effect on fruit set, yield, fruit quality and shoot growth were determined. A comparison of fruit quality from untreated trees in full sun were compared to fruit quality from trees grown under shade net. These trials were repeated over two seasons.

The effect of permanent nets on yield of ‘Larry Ann’ and ‘Midnight Gold’ plums was inconclusive. Fruit maturity was consistently affected. After storage and shelf-life slightly more decay and aerated tissue was found in ‘Midnight Gold’, and to a lesser extent internal browning, and gel breakdown in ‘Larry Ann’. The PGRs applied at the rates used were not very efficient in controlling vegetative growth in both cultivars. As a side effect it was observed that a foliar application of uniconazol and to a lesser extent reduced fruit set in ‘Larry Ann’ plums.

Data is inconclusive. It appears as if yield might decrease under fixed nets over time. No clear effect on harvest maturity and post harvest fruit quality. PGRs at the rates applied in the trials were not effective in controlling vegetative growth.

The trials conducted were not conclusive but a fixed permanent net might result in long term yield reduction and retractable nets should be considered.