## 2 Walnut Blight Prevention  
_Walnut Blight and Conditions_  
Typically, the cycles of walnut blight bacteria are dependent upon weather conditions and rainfall during the growing season. Infrequent rainfall during the spring may lead to monocyclic progress, while frequent spring rainfall tends to favor polycyclic disease epidemics. Rainfalls during late spring (after leaf growth) have been reported to favor the spread of _X. arboricola_ pv. _juglandis_ bacterium, which causes serious damage to trees and is responsible for significant crop losses, which can reach more than 50% of nut drop [19]. All aerial walnut organs, including catkins, female flowers, leaves, and fruit, are infected [3]. Necrotic lesions on the fruit, twigs, and foliage are characteristic disease symptoms. Leaf lesions consist of small water-soaked spots, surrounded by chlorotic halos that extend to become brown necrotic lesions. Fruit lesions begin as tiny, water-soaked spots and develop into pericarp and inner nut tissue necrosis, which results in early fruit drop. After shell hardening, infections often only impact the epicarp [20]. Cankers serve as a source of inoculum for leaves and nutlet infections [4; 21; 22]. Populations of _X. arboricola_ pv. _juglandis_ found on dormant buds serve as the primary inoculum for nut infections [21]. Tissues that have recently been infected can act as secondary sources of inoculum for the pathogen. Pollen released from infected catkins plays a role in pathogen dissemination [2; 21]. The bacterium is transmitted through moisture, particularly through the combined action of wind and rain [23]. The cultivars Chandler and Vina exhibit significant susceptibility to _X. arboricola_ pv. _juglandis_, thus demonstrating the potential of these cultivars to be infected with _X. arboricola_ pv. _juglandis_ under conditions favorable for the disease [5; 21; 24]. The terminal fruitfulness cultivars Milotai, Marbot, Sibisel, and Ronde de Montignac and the lateral fruitfulness cultivars Chandler, Sunland, and Techama were found to be highly susceptible cultivars, making it possible to serve as host responses to bacterial blight infections at different leaf and fruit growth stages [20]. Overall, the degree of infection caused by _X. arboricola_ pv. _juglandis_ bacterium depends on: (a) the quantity of the pathogen present in individual catkin buds and catkins (inoculum); (b) the quantity of walnut blight cankers present on certain walnut varieties; (c) the environmental conditions, such as rain, which play a significant role in spreading bacteria and aiding infection; and (d) the variety, with early leafing varieties being most severely affected. Besides the favorable conditions for the disease, research suggests that pollen released from infected catkins plays a role in pathogen dissemination [21; 22]. Aerial dissemination of infected pollen from diseased catkins may also transmit the bacterium _X. arboricola_ pv. _juglandis_ to pistillate flowers. However, this source of inoculum might be region specific [25] or due to different origins of the propagation material [3]. Up to date new evidence provides data that infections depend on pollen, especially in walnut orchards with varieties for which the catkins emerge before the pistillate flowers, i.e., cv. Chandler. Indeed, pollen is important for spreading bacteria and aiding infection [3]. Even more, the isolation of _X. arboricola_ pv. _juglandis_ in late winter-early spring led to the finding that the primary inoculum is present in buds (overwintering), catkins, and female flowers [4; 21]. So, it is crucial to select walnut varieties resistant to bacterial blight and to implement good orchard management techniques, such as pruning and fertilization, to keep trees healthy and less susceptible to disease. Moreover, one should be aware of pollen released from infected catkins, which contributes to the spread of the pathogen, _X. arboricola_ pv. _juglands_.