EFFECT OF POTASSIUM AND MAGNESIUM FERTILIZATION ON BARLEY PREFERENCE BY THE BIRD CHERRY-OAT APHID RHOPALOSIPHUM-PADI (L.)

The effect of K and Mg on preference of the bird cherry-oat aphid Rhop alosiphum padi (L.) for barley and on suitability of the plants for ap hids was studied in an open hall during three vegetation periods. Plan ts of the spring barley cv. Zenit cultivated in Caslav soil with a low K content and in Ruzyne soil rich in K, were treated with four fertil izer combinations (NP, NPK, NPMg, NPKMg). Under conditions of free hos t choice aphids showed a higher preference for plants growing in K def icient Caslav soil or treated with fertilizers devoid of K (NP, NPMg v ariants), while plants cultivated in Ruzyne: soil rich in K or treated with NPK showed low attractivity. A significant positive correlation was found between plant preference by aphids and their suitability for aphids evaluated by means of artificial infestation. Treatment of the plants with Mg increased their attractivity for aphids and aphid repr oduction while the negative effect on their condition brought about by insect was reduced. Joint application of both elements (NPKMg variant s) increased plant preference by aphids while plant suitability for th e insects was essentially the same as in NPK variants. The mechanism a nd expression of resistance to aphids induced in cereals by the nutrit ional conditions and treatment with different fertilizers are discusse d.