Dahlia flowers - dealing with diseases, insects and pests
Insects affecting Dahlia flowers
The plants of dahlia may be attacked by several pests like Aphids, European corn borer, Leaf hopper, Red spider mites and onion thrips. Besides these, slugs and snails, the chrysanthemum nematodes (Aphelenchoiles ritzemabosi) and white fly (Trialeurodes vaporariorum) may also be a problem.
Several species of aphids like Myzus persicae, Aulacorthum solani, A.circumflexum and Aphis fabae are found on dahlia. They suck the sap from plant tissues and also transmit the viral diseases like mosaic & spotted wilt. Aphids can be controlled by spray of 1% Malathion or Endosulfan at regular interval.
The caterpillar of the European corn borer (Ostrinia nubilalis) is a serious pest. The larvae feed on the young shoot tips and flowers, after which they bore through the stems causing affected parts to wilt. Spray with Monocil @ 1% at weekly interval controls the pest.
Leaf hopper (Empoasca fabae) causes discolouration of the leaf along the margin. Affected area becomes brown and brittle and infected plants show stunted growth. The pest can be controlled by spraying with Malathion or Metacid @ 1% at fortnightly interval.
Red spider mites (Tetranychus urticae) are also serious pests. They feed on the undersides of leaves causing a white speckling and making webs around leaves and buds. Spray of propargite (0.03%) is very effective to control the pests.
Onion thrips (Thrips tabaci) causes flecking of flowers and silvering of leaves.
Diseases affecting Dahlia flowers
Dahlias are susceptible to several fungal diseases like powdery mildew (Erysiphe polygoni, E.cichoracearum), grey mould (Botrytis cinerea) rot and stem rots ( Pythium, Rhizoctonia solani, Sclerotinia sclerotiorum), smut (Entyloma calendulae f.sp. dahliae), bacterial diseases like crown gall (Agrobacterium tumefaciens), bacterial soft rot (Erwinia carotovora) and some viral diseases like mosaic & tomato spotted wilt virus.
Powdery mildew can be controlled by spraying 0.1% Karathan or Bavistin. Leaf blight and Botrytis blight can be effectively checked by spray of Dithan M-45 (Mancozeb) and Captan. In stem rot, soil sterilization with steam or chemicals (Formalin) is very effective. Smuts can be controlled by the use of Dithan Z-78, Blitox and Benlate (Benomyl). Bacterial disease can be prevented by dipping roots in streptomycin solution. Infected roots and crowns of plant should be destroyed and changing the site of planting will also help to check the disease incidence. Mosaic is one of the serious viral diseases transmitted by aphids. During infection, leaves become mottled and produces pale green bunds along the mid- ribs. Plants become stunted and show light yellow spots. The spread of viral diseases can be checked by elimination of infected plants, chemical control of winged aphids and use of virus free planting material.