Rainy season problems in Gerbera production

MANILA, Philippines - Rainy season brings in a lot of problems in Gerbera (African Daisy) Floriculture. Low light intensity and shorter effective day lengths lower the productivity of the plants resulting in lower flower counts and weaker floral stems. In high humidity conditions, low light intensity followed by bright, sunny day results in premature wilting of gerbera flowers.

Gerberas are adaptable to moderately moist soil and dry air. Rainy Season of humid tropical Philippines is simply hostile towards the plant. For Gerberas to perform in the Philippines, it is best grown in cooler areas under plastic canopy. Home growing in warmer areas like Manila or Cebu is possible by placing the plants under the eves of the house where it does not receive direct rains and foliage is kept dry by directing the water onto the soil or media.

The most devastating diseases of Gerberas during rainy season are: 

Phytophthora. This is basically a management problem. The watermold Phytophthora proliferate in rotting leaves and other organic debris in the water. Unclean source of irrigation water is the main cause of the infection and can wipe out the plants in a short period of time. Symptoms include leaves starting to flag down; flowers wilting even when sufficiently irrigated; and rotting of the stem and roots (usually turning dark brown and are soft). Dithiocarbamates (Maneb, Zineb or Mancozeb), Ridomil (Methalaxyl), Fosetyl Aluminum (Alliette), Thiram (Arasan) and Propamocarb (Previcur-N ) may be used for managing the problem. Clean water source and early detection of the problem is the most important measure against this disease.

Leafspot Diseases. These are basically caused by Cercospora, Alternaria, and Curvularia. The main cause of these leafspot diseases is the use of misting or water sprinkling equipment over the foliage. Brown to dark brown or purplish leafspots are round or irregular at first. Lesions eventually become larger with concentric rings and lesions may coalesce to form large brown necrotic areas. Although fungicides can easily control the infection, shifting from overhead irrigation to drip solves the problem and saves the farmer the expenditures on fungicide. 

Destroy all leaves with spots whenever possible. Sanitation plays an important role in management of leafspot diseases. 

Botrytis or Grey mold. This is the most widespread of all diseases in Gerbera. The most visible areas affected are the flower parts (petals and disc flowers). The flowers may leave the farm with the least symptom and develops very fast on transit especially if the flowers were transported with moisture on the surface of the petals. It may take only 2 to 3 days on the florist shelves for the molds to grow into visible grey molds. The molds render the flower unsaleable. Several fungicides are moderately effective for Botrytis: Botran (Dichloran), Saprol (Triforine), Daconil (Chlorothalonil). 

Fungicide treatment together with rigid sanitation practices and avoidance of overhead watering system eliminate Botrytis.

Sweet Potato Weevil. The blessing of rainy season is that the insect and mite population usually go down. The case is reverse for weevils. As their hosts get waterlogged, they move and find their way into the next feeding ground: the Gerbera flowerheads and leafy crowns of Gerberas. The weevils feed directly on the petals and hide in between petals when threatened. Sweet PotatoWeevils may be controlled by spraying Fipronil (Ascend).