Relation between the effects of herbicide glyphosate and the development of fungus Phytophthora nicotineae, in citrus plants

Responsible: Carlos Sichieri
Objectives:
Verify the relation between the effect of herbicide glyphosate and the development Phytophthora nicotineae, in citrus plants.
Material and Methods:
The experiment has being conducted in a greenhouse at ESALQ-USP in Piracicaba with 3 different types of rootstock: Lemon Cravo; Citrumelo Swingle and Tangerine Cleópatra all of then grafted with the American Valência citrus variety. The herbicide glyphosate was applied in the trunk of the plants with a small brush. The experimental delineation used was factorial 2x3 with 5 replications. The treatments were:
· T1 – Without glyphosate (just water)
· T2 – Brushing the trunk of citrus with solution of glyphosate 2%
· T3 - Brushing the trunk of citrus with solution of glyphosate 10%
· T4 – Without glyphosate (just water), and inoculation of fungus Phytophthora nicotineae
· T5 - Brushing the trunk of citrus with solution of glyphosate 2%, and inoculation of fungus Phytophthora nicotineae
· T6 - Brushing the trunk of citrus with solution of glyphosate 10%, and inoculation of fungus Phytophthora nicotineae

With 15 days of interval the citrus plants received 5 brushings of glyphosate solution. The application was made 5 cm above of the grafting point down to the soil surface level, with 1ml of the solution for each application. After the appearing of glyphosate symptoms toxicity, the Phytophthora nicotineae was inoculated in the rootstock 5 cm below of the graft point. The evaluations of the lesions, caused by Phytophthora nicotineae in each treatment, were done in the end of December 2005.

Results:

1. After 5 applications, symptom of glyphosate toxicity appeared in the treatment 2% and 10% of glyphosate concentration. Or glyphosate applied in the trunk of the plant (as happen in commercial orchards) can pass through trunk epidermis and move to the tip of upper branches.

2. There was observed no effect of glyphosate on Phytophthora nicotineae development.