{"id":62055,"date":"2025-02-21T13:32:30","date_gmt":"2025-02-21T13:32:30","guid":{"rendered":"https:\/\/metos.global\/?p=62055"},"modified":"2025-03-13T13:57:22","modified_gmt":"2025-03-13T13:57:22","slug":"weather-variability-crop-health","status":"publish","type":"post","link":"https:\/\/metos.global\/en\/weather-variability-crop-health\/","title":{"rendered":"Weather – It\u2019s The Variability That\u2019s Hard To Farm With – PART III – Crop Health"},"content":{"rendered":"\t\t
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Weather – It\u2019s The Variability That\u2019s Hard To Farm With<\/h2>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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PART III - CROP HEALTH<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Author:<\/b> Guy Ash, Global Training Manager, Pessl Instruments<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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In Part I<\/strong><\/a><\/span> of our Weather – It’s The Variability That’s Hard To Farm With<\/strong> series, we discussed the critical role that localized weather data and precipitation play in effective farm management. Part II<\/strong><\/a><\/span> shifted focus to another crucial weather variable – temperature, and how it impacts crop growth and farm operations.<\/p>

Now, in Part III, we explore the influence of relative humidity and leaf wetness on disease pressure, spraying operations (Delta T), and overall crop management. Additionally, we examine wind speed, direction, and gusts, shedding light on their impact on spraying efficiency, lodging risk, and drying conditions. The key takeaway? Understanding these microclimatic factors through site-specific weather monitoring is essential for making informed decisions and safeguarding crop health.<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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RELATIVE HUMIDITY AND LEAF WETNESS: impacts disease pressure\/risk, spraying operations (Delta T)<\/h3>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Relative humidity (%), as the name implies, is relative to the air temperature. A volume of air at 30 \u00b0C (86 \u00b0F) will hold far more water vapor than air at 10 \u00b0C (50\u00b0F), hence the term of relative humidity. Relative humidity values over 95% are typically used in disease models<\/a><\/span> to predict infection conditions.<\/strong> Leaf wetness sensors mimic how a leaf will wet and dry with humid and wet conditions. This is used to look at periods of time when the leaves are wet, which is used in disease model applications. Before and during rain events you will see the leaf wetness values become active.<\/p>

Placement of the leaf wetness in the crop canopy is critical since it mimics the wetting and drying of a leaf. In a thick canopy, a microclimate of warm, humid conditions exists, which drives the environmental conditions for disease development<\/a><\/span>. If it\u2019s placed outside the canopy, then the periods of leaf wetness will be less. Relative humidity sensors are typically part of the air temperature sensor<\/a><\/span> and installed 1.5 meters or about 4 \u00bd feet.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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In the picture: Relative Humidity sensor installed at standard meteorological height of 1.5 meters or about 4 \u00bd feet and Leaf Wetness sensor installed in the canopy of a fruit crop<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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HOW DOES RELATIVE HUMIDITY OR LEAF WETNESS IMPACT CROP MANAGEMENT?<\/h3>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Relative humidity and leaf wetness vary greatly over a small spatial distance because of the nature of precipitation events and the type\/thickness of crop canopy. As discussed above relative humidity is important in the calculation of Delta T for spray applications<\/a><\/span>. In addition, site-specific relative humidity and leaf wetness is very important in the prediction of disease pressure or risk for various crops<\/strong>.<\/p>

Most crop disease models<\/a><\/span> use time periods of various relative humidity levels (%) or leaf wetness periods (minutes) in relationship to temperatures. Simply put, crop diseases require the right environmental conditions to develop into an epidemic<\/strong>, hence the need for site-specific measurements. The illustrations below clearly show that a weather station<\/a><\/span> that isn\u2019t in the field, will not reflect the actual conditions for disease pressure\/risk. The two stations are only 1 \u00bd km or 1 mile apart (one in the field, the other under grass) with the field station showing long infection events with high pressure\/risk. These differences were further confirmed with an on-farm case study of Fusarium in wheat<\/a><\/span><\/strong>, where the field IoT device predicted a higher risk than the government station that was 10’s of km away. It\u2019s not that the models are different, just that the data from the field reflects the actual conditions.<\/p>

Cost of FHB Damage:<\/strong> With fusarium head blight (FHB) disease severity levels varying between 0.5%, 1.2% and 2.2%, downgrading of Canadian Western Red Spring (CWRS) from #1 to #2 or #1 to #3 or #1 to feed on a 55-bushel acre crop has resulted in $12, $35, and $100 of lost farm income per acre in Western Canada.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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In the picture: Biological factors for Disease Development<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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In the picture: Importance of Site-Specific Weather Observations<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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WIND SPEED\/DIRECTION AND GUSTS: impacts spray operations, lodging, drying conditions, evapotranspiration<\/b><\/h3>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Wind speed, gust and direction are usually shown in kmh or mph and degrees or cardinal directions (e.g., northeast). In spray operations, wind direction determines whether droplets travel toward the target or toward unintended downwind areas such as open water, sensitive crops, or areas of human activity.<\/strong> Wind speed affects the distance a droplet will travel before it is deposited on the target \u2013 deposition.<\/p>

Wind speed\/direction is always used in conjunction with Delt T for spray applications, by using the in-field weather station<\/a><\/span> and a field specific forecast<\/a><\/span>:<\/p>