Orchard Management in Extreme Climates: Responses to La Niña in Chile

ARTICLE

All the latest forecasts agree that July and August will bring dry weather, signaling the retreat of El Niño and the return of La Niña for an indefinite period. With this significant change, Chile will once again face a semi-arid climate, increasing stress and bringing cold winters and springs back into the picture.

Almost 10 years ago, the central valley suffered a terrible spring frost, just after the national holidays, with catastrophic results for newly set fruit on deciduous trees. It is very likely that this situation will repeat itself this spring with the arrival of La Niña, requiring orchards to be prepared for the damage caused by the cold. While winter frosts can cause the loss of hanging fruit and new flower buds, affecting production for two seasons, cold springs can also be dramatic, as they generate hidden damage that ends up affecting the swollen bud or the beginning of the cauliflower stage. Frost damage is visible, but cold damage, which usually shows coppery-colored spots on the foliage, could affect floral induction, making it difficult to differentiate the buds that will produce the 2024 flower. Initially, this problem is not visually detectable, but as the panicles elongate, the flowers open and fall off rapidly. In some cases, the leaves don't even open, resulting in poor fruit set and early defoliation. If the leaves fall off at the beginning of flowering, the new panicles will be malnourished at full bloom, as they won't receive the mobile nutrients stored in the foliage. Furthermore, in a cold spring, the root system is likely to develop later, leading to fruit abortion due to malnutrition.

We must take advantage of the new technology being developed in meteorology, delivering accurate forecasts 30 days before any climatic anomaly occurs, giving us time to react and take the following measures in the face of the imminent cold weather that is coming:

1. Begin to replenish the nitrogen reserves in both the foliage and roots by applying amino acids. While urea is commonly applied in winter and spring, it's well known that this fertilizer becomes ineffective when temperatures drop, failing to restore reserves. It's better to switch from nitrogen sources to fast-release and readily absorbed amino acids to effectively increase plant reserves. If we enter winter with low reserves, the cold will weaken the orchard's immunity, leading to poor spring growth and premature defoliation.

2. Water cautiously during winter and early spring, as it is important to improve soil oxygenation and temperature to encourage rapid root growth. If watering at the beginning of spring causes waterlogging, root activity will be very low, and plants with poor nutrition will be more susceptible to cold.

3. Work with nutrients that rehydrate tissues and strengthen cell walls. During winter and early spring, potassium (K) should be present in higher proportions, as cold damage causes dehydration. If the tissue becomes dehydrated, it can be rehydrated to promote rapid recovery. Calcium (Ca) and silicon (Si) are essential for strengthening tissues. It is known that calcium is absorbed when the plant has root growth, and many orchards likely experience reduced root activity during the winter. Supplement the calcium cation with silicon by applying potassium silicate or diatomaceous earth via irrigation. This will allow it to slowly transform into monosilicic acid through bacterial activity (biosilication) and be absorbed by the roots. Silicon has several effects within the soil and should be applied before or after a stressful event.

4. Develop biological fertilization, as it is more efficient, strengthens tissues, and boosts plant immunity, increasing tolerance to abiotic stress. Orchards using biological fertilization programs that include high doses of carbon, seaweed extract, amino acids, microbial consortia, and biofertilizers develop cells with higher solute concentrations, lowering the freezing point. Saline fertilization is very inefficient and produces weak, succulent tissues that show damage even at 0°C, while tissues developed with biological fertilization show no frost damage even at -4°C for extended periods. This effect has been documented in the literature for some time, but the agricultural world, with its very traditional management practices, continues to prioritize nitrogen over other nutrients, causing damage and imbalances in fruit growth and production.

5. Apply Complete Floral Nutrition from the beginning of the cauliflower stage, as the plants will be hormonally suppressed due to the cold, and nutrients will arrive late to nourish the new embryos. Consider 3-4 applications to cover the entire flowering period and delay flower opening, as October is likely to have cold nights. Floral Nutrition, in addition to feeding the new blooms and fruit set, prevents premature defoliation and strengthens the panicle, resulting in a longer and thicker peduncle that better tolerates abiotic stress, thus preventing fruit abortion.

6. If unfortunately measures are not taken in time and the orchard is affected by frost or cold, immediately after the events, the recovery capacity can be appealed to by favoring the rehydration of the tissues by applying high quality K together with Chitosan to repair the micro wounds that form in the tissues exposed to the cold.

These same management practices used to increase resistance to cold are also recommended when heat waves or water stress are forecast. High temperatures and wind can often cause stress and dehydration, even with proper irrigation, but after the stress subsides, plants can recover their growth and catch up on their fruit size if the recommended suggestions are followed.

It seems that normal years no longer exist and we must be prepared to live with climatic anomalies on different dates of the year, managing orchards in good condition so that they develop a rapid recovery after each stress.