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Data-Driven Crop Management

Forecasting and early warning for pests and diseases: from weather data to a spray decision

29 September 2026 updated · 6 min read · 20 views

When to spray matters as much as what to spray. A treatment applied too early is wasted; one applied too late cannot stop the damage. Forecasting and early warning systems tie that timing to weather data, the biology of the pest and counts made in the field. This guide explains how these systems work and how they are applied in citrus, a leading crop in Kozan, and in cotton, which both regions grow.

The EU framework: monitor first, decide against a threshold

The EU Directive on the sustainable use of pesticides (2009/128/EC) requires Member States to ensure that professional users have access to tools for pest monitoring and decision making, and to advice on integrated pest management. Three of the directive's eight general principles deal directly with this: harmful organisms must be monitored through field observation and, where feasible, scientifically sound warning, forecasting and early diagnosis systems; the decision to treat must rest on monitoring results and on robust threshold values defined for the region, crop and climatic conditions; and the success of each measure should be checked against pesticide records and monitoring results (EU, 2009). As an EU Member State, Greece is bound to apply these principles; in Türkiye the same logic appears in the sampling methods and economic thresholds of the Ministry's integrated pest management technical guidelines.

What data do the models use?

Degree-days

Insects and many pathogens develop at a rate set by temperature. According to the University of California Statewide IPM Program (UC IPM), the heat an organism needs, between its lower and upper thresholds, to develop from one point in its life cycle to another is measured in degree-days. The lower threshold is the temperature below which development stops; the upper threshold is the temperature above which development slows or stops. The date to start accumulating degree-days, the biofix, varies by species and is usually a biological event such as planting, first trap catch or first sighting of the pest. UC IPM recommends the single sine method, which fits a sine curve to the day's minimum and maximum temperatures, with a horizontal cutoff at the upper threshold (UC IPM).

Leaf wetness and humidity

For fungal diseases, infection depends largely on how long the leaf surface stays wet and at what temperature. UC IPM's disease model database describes a model as a mathematical description of the interaction between environment, host and pathogen; the main variables that weather stations track are air temperature, relative humidity, hours of free moisture and rainfall. The same source adds an important caution: before using a model that has not been validated for a location, test it under local conditions for one or more seasons (UC IPM).

A concrete citrus example is Alternaria brown spot. According to the Ministry's citrus guideline, the disease is common especially on Minneola, tangelo and hybrid mandarin varieties, and rain, sprinkler irrigation, over-irrigation and dew all favour it. The guideline advises against sprinkler irrigation that leaves the canopy wet for long periods, recommends the first spray when shoots reach 5-10 cm and first symptoms appear, and continuing until fruit reaches about 4 cm in diameter (TAGEM, 2022). The University of Florida (UF/IFAS) citrus production guide recommends timing sprays for the same disease with ALTER-RATER, a weather-based model. According to the guide, brown spot is most severe when rainfall exceeds 0.1 inch (about 2.5 mm), daily leaf wetness exceeds 10 hours and average daily temperature is between 68 and 83 °F (about 20-28 °C); a fungicide is applied once the model threshold is reached (UF/IFAS, 2026).

Türkiye's forecasting and warning system

The Ministry's forecasting and warning system determines and announces the right time for control once a disease or pest is present where a crop is grown. Field stations measure air and soil temperature, relative humidity, rainfall, leaf wetness, pressure and wind and send the data to a central computer; the resulting notices go to growers by text message and e-mail. According to the Ministry's 2014 leaflet, the system was first researched in apple orchards and vineyards in the early 1980s, and its most common targets are downy mildew and the European grapevine moth in vineyards, apple scab and codling moth in apples, and fire blight in pears. At the time of the leaflet it served about 2 million decares (200,000 ha) with 274 devices in 47 provinces. To receive notices, growers register their mobile phone and e-mail with the provincial or district directorate (MoAF, 2014).

The agricultural weather forecast pages of the Turkish State Meteorological Service (MGM) also show the daily sum of effective temperatures used in pest and disease control and in timing the harvest, as well as the hours and days that are or are not suitable for spraying. The site notes that the data come from automatic stations and have not been quality controlled (MGM), so they are best read together with observations in the orchard.

Citrus: Mediterranean fruit fly

The Mediterranean fruit fly (Ceratitis capitata) can complete 10-12 generations a year in Türkiye's Mediterranean region; damage varies from 5% to 80% depending on the area, and as a quarantine pest it has zero tolerance in export markets (TAGEM, 2022). The Ministry's citrus integrated pest management guideline sets out the decision chain as follows:

  • Monitoring: one monitoring trap per 8-10 decares (0.8-1 ha), with adult catches recorded regularly. Traps hang on the south to south-east side of the tree, 1.5-2 m above ground, in partial shade, with openings kept clear of leaves.
  • Start: control begins when effective temperatures reach 369 degree-days or when the first adult appears in a monitoring (trimedlure) trap; fruit is checked for stings as it starts to ripen.
  • Threshold: between August and October, when monitoring traps catch 3 or more adults per day in mandarins, or 6 or more per day in oranges and grapefruit, and the fruit has reached colour break, bait spot sprays on part of the canopy or mass trapping are applied.
  • End: spraying stops when the daily mean temperature falls below 16 °C; lemon orchards are not considered to need spraying.

Cultural measures are part of the guideline too: fallen infested fruit should be collected and buried at least 50 cm deep, and no fruit should be left on the trees after harvest (TAGEM, 2022). Asking the provincial or district directorate which base temperature and start date are used for the 369 degree-days keeps your own station-based calculation in line with official notices.

Cotton: pink bollworm

For the pink bollworm (Pectinophora gossypiella), the Ministry's cotton guideline does not recommend chemical control; the pest is managed through cultural measures, biotechnical methods and the Turkish regulation on pink bollworm in cotton plantings (TAGEM, 2022). The decision tools are:

  • Pheromone traps: delta or funnel pheromone traps track moth flights; the guideline gives one trap per 80 decares (8 ha), two per field. The recommended products also include pheromone dispensers at 25 per decare.
  • Rosette flower counts: 50 decares (5 ha) form one unit; in each unit, rosette flowers are counted along 25 m of row at 5 points at least 15 m apart and multiplied by 10 to give rosette flowers per decare. Counts are made once each at 5 days after first flowering, when two thirds of the bolls are mature, and after harvest.
  • Boll checks: once two thirds of the bolls have matured, 100 bolls are picked at random while walking diagonally across the unit, cut open and checked for larvae, and infested bolls are counted.

The cultural measures follow a calendar: under the regulation, stalks carrying unopened bolls must be used up by the end of March and ginneries must finish work by 31 March; after harvest, stalks should be cut with a stalk shredder and ploughed in deeply, and certified, delinted seed free of pink bollworm should be used (TAGEM, 2022). Because chemical control is not recommended, trap and count data in cotton serve more to track whether these measures are working than to time sprays.

In the field

  1. Sign up for warnings: give your phone number and e-mail to the provincial or district directorate.
  2. Record trap counts by date, trap number and count, and note the day's temperature and rainfall next to them.
  3. Do not treat before the threshold is crossed, and check the effect of each treatment with the next count.
  4. If you plan your own station, see the platform's IoT guides for sensor siting and maintenance; frost risk and early warning in citrus are covered in a separate guide.

Sources

  1. European Parliament and Council, 2009. Directive 2009/128/EC establishing a framework for Community action to achieve the sustainable use of pesticides (Article 14, Annex III) (accessed 29 September 2026)
  2. T.C. Tarım ve Orman Bakanlığı, TAGEM, 2022. Turunçgil Entegre Mücadele Teknik Talimatı (accessed 29 September 2026)
  3. T.C. Tarım ve Orman Bakanlığı, TAGEM, 2022. Pamuk Entegre Mücadele Teknik Talimatı (accessed 29 September 2026)
  4. T.C. Gıda, Tarım ve Hayvancılık Bakanlığı, Gıda ve Kontrol Genel Müdürlüğü, 2014. Bitki Sağlığında Tahmin ve Uyarı Sistemleri (broşür) (accessed 29 September 2026)
  5. Meteoroloji Genel Müdürlüğü. Tarımsal Hava Tahmini: açıklamalar (accessed 29 September 2026)
  6. University of California Statewide IPM Program (UC IPM). Degree-days: concepts (accessed 29 September 2026)
  7. University of California Statewide IPM Program (UC IPM). Plant disease models database (accessed 29 September 2026)
  8. Dewdney, M. M., UF/IFAS Extension, 2026. 2026-2029 Florida Citrus Production Guide: Alternaria Brown Spot (CG021) (accessed 29 September 2026)
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