The study of citrus infestation by the black scale Parlatoria ziziphi Lucas 1853 (Homoptera, Diaspididae) is realized between 2012 and 2013 on two citrus varieties (Thomson and Portuguese) in El Fehoul station in Tlemcen in the NorthWest of Algeria. This study shows that Parlatoria ziziphi is present in both varieties and the upper surface of leaves is is always more infested than the lower surfacess. In terms of leaves infestation rates, it's very important at the southern exposure and the center of the plot for Thomson variety and with 100 % in the southern and northern exposure of the Portuguese variety. The rate of fruit fruit infestation is the most important in the south with 87.9 % for Thomson variety and 79 % for the Portuguese variety. The infestation rate of the leaves does not change after harvesting the fruit. This species of scale insect is cosmopolitan and it attacks many species of Citrus family. It is also very common on citrus in Algeria.

A greenhouse experiment was conducted to investigate the effect of different levels of NaCl salt on tomato upon B. cinerea infection the causal agent of gray mold disease. The disease assessment was recorded after inoculation by using the scale based on percentage leaf area affected, and the growth of the plants was recorded for each treatment. Three weeks after inoculation by conidial suspension, the estimated disease severity on plants of tomato was 35.18% compared to the control. The highest incidence disease increase of gray mold (39.21%) was obtained with using 300 mM of NaCl after inoculation with B. cinerea compared with the other concentrations and as well as distilled water. Under severe salt stress (150 and 300mM) increased susceptibility of gray mold disease severity were observed in plants inoculated with B. cinerea, while under mild salt stress (50mM of NaCl) this effect was reversed. The treatment of plant by B.cinerea has reduced the growth of the aerial part of tomato plants (39.06%) after three weeks inoculation compared to the control. Three levels of NaCl (50, 100 and 150mM) increased respectively the plant height from 12.73 to 29.84%, 0.28 to 27.16% for the fresh eight and 5.75 to 33.35% for dry weight compared to the plants inoculated and irrigated by distilled water. NaCl addition at 300mM on plants inoculated with B. cinerea decreased the height, fresh weight and dry weight at 0.99, 4.45 and 11.01% respectively.