Quite an interesting hay and haylage harvesting season so far this year. Across the state all forage producers have noted how advanced first cutting was this year. In parts of the southern region of the state most of first cutting of alfalfa has been made as haylage and in the central and northern regions harvest is simply waiting for ideal weather, if only Mother Nature will cooperate.

Since early May there has not been very good dry hay making weather. Most of the forage that has been harvested to date has been stored as haylage. In many cases where wet hay harvest is not possible the crop remains standing and is rapidly losing feed quality. Weather patterns in the next few days do not indicate a high probability of long periods of dry hay making weather but between rain events there may be small windows of harvest opportunities.

What effect does rain have on hay crops? Agronomists who have studied this note that the answer is not as simple as first thought. The actual impact of rain on hay crops depends on a few different factors including: how soon after cutting the crop is rained on, the length of the rainfall, the intensity of the rain and the type of forage crop.

The most damage to a hay crop from rainfall would be to have a nearly dry alfalfa crop that got rained on for a long time period with a heavy rain event. The closer to cutting that rain occurs results in less losses. In fact many producers have mowed hay during the tail end of rain events to get a jump on good weather that follows a cold front. In this situation mowing in a narrow windrow and then using a tedder soon after is important to get forages drying down rapidly.

Of course, the longer a rain event occurs on cut forages the greater the losses. When forages are wet (>30% moistures) the plant continues to respire even after mowing. This respiration process consumes plant sugars and other carbohydrates that reduce whole plant digestibility and feed values. An interesting note is that these same plant sugars are necessary for making high quality haylages. Frequently, rained on haylages result in poor fermentation and have less than desirable storage potential.

The intensity of a rain can affect forage losses also. A heavy downpour is more damaging to a crop than a slow rain event. Heavy rains again will wash out the desirable cell components resulting in poor quality feeds.

Finally, different crops will vary in their tolerance to rain events. Legumes, with many small leaves, are at a high risk for leaf loss from rain compared to grass type plants. Since highest plant quality is related to the amount of leaves in the forage efforts to retain leaves becomes critical.

So in summary the worst case scenario for rain events would be to have a long, high intensity rain to occur just prior to an alfalfa crop being ready to bale. The best case, if there is such a best case of rained on hay, would be a grass hay crop getting a light rain for a short time period immediately after mowing. Now, do you trust your weather man?

Source: Paul H. Craig, Dauphin County Pennsylvania Extension