Phytophthora infestans causes late blight in potatoes and also infects tomato, eggplant, pepper, and other solanaceous plants. The disease is more severe in humid conditions and if left untreated, has the potential to wipe out an entire crop. Blight is believed to be responsible for the famous Irish potato famine in the 19th century.

The disease symptoms include lesions on the stems, leaves, and tubers. The infected tubers are also susceptible to secondary infections from other microbes. Infected leaves develop dark spots that spread and eventually become brittle, and white mildew will grow on the underside of the leaf in high humidity.

There are many subspecies of P. infestans and no potato varieties are resistant to all of them. Removal of infected seed tubers and foliar fungicide are key to controlling this disease. The use of disease free seed tubers is critical to reducing the spread of late blight because P. infestans overwinters as mycelia in infected tubers.

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Wheat represents one of the most important crops in Canada by area farmed and metric tonnes of total production. There are two major fungal pathogens that affect wheat; Stripe rust (Puccinia striiformis) and Fusarium head blight (Fusarium graminearum). Stripe rust can cause losses of up to 40% in susceptible varieties of wheat. Symptoms include defoliation, shriveling of the seed, and reduced kernel numbers.

Fusarium head blight (FHB) is considered the most economically important disease affecting wheat; damage from it impacts yield and quality, commonly resulting in grade loss.  The fungus produces the toxin DON (also known as vomitoxin) which can cause feed refusal in livestock and vomiting in humans and animals, because of this only very low concentrations are tolerated in cereals.

Sclerotinia sclerotiorum causes stem rot, also known as white mould, in canola. Stem rot is one of the most destructive diseases of canola. The symptoms of the disease include browning of the petals, whitish-grey lesions on the stems, brittle stems, and discoloration. Canola is under threat from S. sclerotiorum when it is in bloom because the flowers are the site of infection for the fungus.  In two main species of canola, Brassica rapa and B. napas  the flowering period last for 14 to 21 days in both species. Crop losses are highly variable depending on the weather and the timing of infections, and losses can reach as high as 50% per infected plant.  Foliar fungicides remain the main control strategy for stem rot.

Soy is the fourth largest field crop in Canada by hectares grown and has doubled in production from 2009 to 2018. In the USA, Soy is the second largest field crop by hectares and is only surpassed by corn. Asian Soy Rust (Phakopsora pachyrhizi) and to a lesser extent New World Soy Rust (Phakopsora meibomiae) affects soy crops on every continent as no known resistant varieties of soy exist. Symptoms are most commonly observed on leaves first and result in significant defoliation. Lesions are small yellow and irregularly shaped spots. Yield losses can be severe with up to 80% being reported.

With legalization in Canada and some states in the USA, Marijuana cultivation is booming. With outdoor field cultivation recently permitted there will be many challenges to overcome including fungal pests. Powdery mildews, such as Golovinomyces cichoracearum are an extremely common pest on Marijuana plants and causes early leaf drop and reduces flower quality. Gray Mold (Botrytis cinerea) is also commonly found on Marijuana and has severe impact on the plant. Lesions start as small discolorations on the leaves or bud and can rapidly grow into a grey mycelial tissue that can spread and destroy a crop.

Mildew is the most widespread disease affecting grapevines globally and comes in two forms; Downy and Powdery. Downy mildew is caused by the fungal organism Plasmopara viticola and causes damage to the vines by rotting inflorescences, berries, clusters and shoots. Premature defoliation of vines due to foliar infections can predispose the vine to winter injury which can take several years to recover from. Uncinula necator (syn. Erysiphe necator) is the fungal organism responsible for powdery mildew and can infect all green parts of the grapevine. Infected berries often are misshapen or have rusty spots on the surface and may split open. Up to 100% crop loss is possible if this disease is not managed. Fungicides for mildews should used before infection occurs.

Corn suffers from a variety of diseases that can reduce quality of the grains. Gibberella Ear rot caused by Gibberella zeae is a mycotoxigenic fungus, producing vomitoxin and zearalenone. Tar spot is an emerging disease that can cause significant yield loss if the conditions are favourable. Caused by the fungus Phyllachora maydis, it appears as small, raised, black spots scattered across the upper and lower leaf surfaces.

There are several economically important diseases of strawberries. Fruit diseases such as Gray mold (Botrytis cinerea), Powdery Mildew (Podosphaera aphanis) and Anthracnose (Colletotrichum
acutatum) can causes loss of fruit quality and yield. Fusarium wilt (Fusarium oxysporum  f.sp. fragariae), Verticillium Wilt (Verticillium dahlia), and Charcoal Rot (Macrophomina phaseolina) are emerging diseases due to the elimination of methyl bromide for fumigation in some jurisdictions.

Blueberries are susceptible to several diseases that are of concern to growers; Powdery mildew (Erysiphe vaccinii) and Alternaria alternata / tenuissima which can cause leaf spot and fruit rots.

Phytophthora blight (Phytophthora infestans) and Downy mildew (Pseudoperonospora cubensis) are two important diseases that affect most of the members of the Curcurbit family.

Sugar beets are susceptible to several disease that can greatly reduce yield. Powdery mildew (Erysiphe betae), downy mildew (Peronospora farinosa) and Cercospora leaf spot (Cercospora beticola) can all cause serious damage to the leaves, causing major reductions of yield.